The latest version of the Tangled Bank has been posted on _Paddy K_ [Tangled Bank #92].
Welcome welcome one and all, to the eighty-twelfth edition of the ancient and worthy Tangled Bank Blog Carnival. And let the games begin…
Welcome welcome one and all, to the eighty-twelfth edition of the ancient and worthy Tangled Bank Blog Carnival. And let the games begin…
[Hat Tip: John Dennehy, who has other suggestions for improvement.]
[Photo Credit: A rough diagram of the Immune system]
OTTAWA -- The Conservative government will not co-sponsor a United Nations resolution calling for a global moratorium on the death penalty, breaking with a nearly decade-old tradition.Yeah, right. This represents a substantial shift in policy for the Canadian government. It's consistent with another change recently announced whereby Canada will no longer oppose the execution of Canadian citizens in foreign countries.
An official with the Foreign Affairs Department says Canada will vote in favour of the resolution when it comes to the floor of the UN General Assembly in December, but will not sponsor it.
"There are a sufficient number of co-sponsors already, and we will focus our efforts on co-sponsoring other resolutions within the UN system which are more in need of our support,'' said Catherine Gagnaire.
Last week, Public Safety Minister Stockwell Day surprised the House of Commons by announcing that Canada will not oppose the execution of a Canadian citizen on death row in Montana for two murders. Day said the new policy will apply to "murderers'' such as Ronald Allen Smith who have had a fair trial in a democratic country. (Doesn't the idea of Stockwell Day as "Public Safety Minister" just want to make you cry? )One of those countries is surely the United States of America. A country that executes Canadian citizens and has voted against the UN Human Rights resolution every single time.
The government has not specified which countries it considers democracies.
What we don’t know is whether any non-intelligent means can generate complex biological systems. A single observation of a complex biological system generated by a non-intelligent cause will falsify the biological ID hypothesis.Now I see the logic. All the evidence for the natural evolution of complex biological systems doesn't count for a damned thing. You have to actually see something like that evolve with your own eyes before you can believe it. If you don't actually witness the thing then it's logical to assume that it doesn't exist. Right?
P.falciparum replicating billions of trillions of times in the past few decades represents the largest search to date for a “black swan”. This is orders of magnitude more replications than took place in the evolution of reptiles to mammals wherein there are many exceedingly complex biological systems that separate them. If P. falciparum had been seen generating any complex biological systems such as those that distinguish mammals from reptiles then it would have falsified the ID hypothesis. None were observed. This doesn’t prove ID but it certainly lends strong support to it. All perfectly scientific.Don't you just love creationist logic? Just because we haven't seen any complex biological systems spring naturally into existence in Plasmodium falicparum it follows that it's impossible for such thing to happen. Therefore Intelligent Design Creationism is strongly supported. QED.1.
1. The argument would make some sense if evolution predicted that complex biological systems should evolve in protozoa every few hundred years. Since evolution predicts no such thing then nothing has been demonstrated except that Intelligent Design Creationists are IDiots. But we already knew that.
[Photo Credit: photo by Graham Stephinson at canberabirds]
And so I ask, on what basis do you draw the sharp moral line between "humans" and "animals", "human rights" and "animal rights", "us" versus "them"? What rational argument do you bring in defense of speciesism? Perhaps you argue that only humans are capable of suffering, or that our intellectual capabilities are of a different kind from those of other animals. As Dawkins has noted, neither is compatible with what we understand about evolutionary history.I don't have an answer to these questions even though I've been thinking about them far longer than youngsters like Ryan Gregory.
[Photo Credit: Smithsonian National Zoological Park]
Note to students at the University of Toronto: This could be on the The University Exit Exam].
While most Canadians scurry around their homes changing their clocks back to standard time this weekend, the clock-keepers of Parliament Hill will only sit and wait.At the risk of sounding stupid, why doesn't the technician just advance the clock eleven hours?
At 2 a.m. Eastern Daylight Time on Sunday, a Public Works employee will open a glass housing and flip a switch, bringing the 50-year-old mechanism that runs the Peace Tower clock, with its four faces, to a halt....
For 60 minutes, the technician will just wait and then will restart the 1950s-era electric motor drive that runs the big clock, several levels overhead, at exactly 2 a.m. Eastern Standard Time, according to the National Research Council time signal
They need to wait out the hour because the old motor drive only goes forward, says Brian Cook, the Public Works property manager for Parliament Hill.
You poor Americans -- you have a leader whose party doesn't even have a majority, who's submitting one vile bit of legislation and one horrendous nomination after another, and you have an "opposition" that just rolls over and plays dead on all of it. I feel so sorry for you. Now up here in Canada, we ... we ... um ... actually, never mind.
I should have thought about that argument a bit harder, really.
In the end, Watson's decided to return home, so no meetings occurred, a move that has dismayed many scientists who believed that it was vital Watson confront his critics and his public. 'What is ethically wrong is the hounding, by what can only be described as an illiberal and intolerant "thought police", of one of the most distinguished scientists of our time, out of the Science Museum, and maybe out of the laboratory that he has devoted much of his life to, building up a world-class reputation,' said Richard Dawkins, who been due to conduct a public interview with Watson this week in Oxford.I agree with Dawkins. Watson was stupid to make those remarks but they were perfectly consistent with a lifelong career of being as politically incorrect as possible in today's society. Does that make him a racist whose career should be terminated?
Dawkins's stance was supported by Blakemore. 'Jim Watson is well known for being provocative and politically incorrect. But it would be a sad world if such a distinguished scientist was silenced because of his more unpalatable views.'
Nor is it at all clear that Watson is a racist, a point stressed last week by the Pulitzer-winning biologist E O Wilson, of Harvard University. In his autobiography, Naturalist, Wilson originally described Watson, fresh from his Nobel success, arriving at Harvard's biology department and 'radiating contempt' for the rest of the staff. He was 'the most unpleasant human being I had ever met,' Wilson recalled. 'Having risen to fame at an early age, [he] became the Caligula of biology. He was given licence to say anything that came into his mind and expected to be taken seriously. And unfortunately he did so, with casual and brutal offhandedness.'This is a clear case of political correctness out of control. I'm embarrassed to be associated with the people who attacked Watson and I admire Dawkins (and Blakemore) for standing up to them.
That is a fairly grim description, to say the least. However, there is a twist. There has been a rapprochement. 'We have become firm friends,' Wilson told The Observer last week. 'Today we are the two grand old men of biology in America and get on really well. I certainly don't see him as a Caligula figure any more. I have come to see him as a very intelligent, straight, honest individual. Of course, he would never get a job as a diplomat in the State Department. He is just too outspoken. But one thing I am absolutely sure of is that he is not a racist. I am shocked at what has happened to him.'
The Panda’s Thumb, on the other hand, is entirely low-market; the men who contribute to the blog all have some vague technical background – computer sales, sound mixing, low-level programming, print-shops or copy centers; they are semi-literate; their posts convey that characteristic combination of pustules and gonorrhea that one would otherwise associate with high-school toughs, with even the names – Sir Toejam, The Reverend Lenny Flank – suggesting nothing so much as a group of guys spending a great deal of time hanging around their basements running video games, eating pizzas, and jeering at various leggy but inaccessible young women.
Darwin’s theory is plain nuts. It is not supported by the evidence; it has no organizing principles; it is incoherent on its face; it flies against all common experience, and it is poisonous in its implications.
And another thing. It is easy to understand. Anyone can become an evolutionary biologist in an afternoon. Just read a book. Most of them are half illustrations anyway. It’s not like studying mathematics or physics, lot of head splitting stuff there.
But Dawkins …
DB: An interesting case, very louche – fascinating and repellant. Fascinating because like Noam Chomsky he has the strange power effortlessly to command attention. Just possibly both men are descended from a line of simian carnival barkers, great apes who adventitiously found employment at a circus. I really should look at this more closely. Repellent because Dawkins is that depressingly familiar figure – the intellectual fanatic. What is it that he has said? “It is absolutely safe to say that, if you meet somebody who claims not to believe in evolution, that person is ignorant, stupid or insane (or wicked, but I’d rather not consider that)”. Substitute ‘Allah’ for ‘evolution,’ and these words might have been uttered by some fanatical Mullah just itching to get busy with a little head-chopping. If he ever gets tired of Oxford, Dawkins could probably find a home at Finsbury Park.
It is a matter of attitude and sentiment, Look, for thousands of intellectuals, becoming a Marxist was an experience of disturbing intensity. The decision having been made, the world became simpler, brighter, cleaner, clearer. A number of contemporary intellectuals react in the same way when it comes to the Old Boy – Darwin, I mean. Having renounced Freud and all his wiles, the literary critic Frederick Crews – a man of some taste and sophistication – has recently reported seeing in random variations and natural selection the same light he once saw in castration anxiety or penis envy. He has accordingly immersed himself in the emollient of his own enthusiasm. Every now and then he contributes an essay to The New York Review of Books revealing that his ignorance of any conceivable scientific issue has not been an impediment to his satisfaction.The problem with Berlinski is that he's a fuzzy-headed idiot on some things but on others he hits a little too close to the mark for my comfort level. He's the Christopher Hitchens of the Intellligent Design movement.
Another example – I’ve got hundreds. Daniel Dennett has in Darwin’s Dangerous Idea written about natural selection as the single greatest idea in human intellectual history. Anyone reading Dennett understands, of course, that his acquaintance with great ideas has been remarkably fastidious. Mais, je divague …
In the case of both Crews and Dennett, it’s that God-awful eagerness to explain everything that is the give-away. The eagerness is entirely academic or even literary. But, you know, what sociologists call prole-drift is present even in a world without proles. Look at Christopher Hitchens – very bright, very able. Just recently he felt compelled to release his views on evolution to a public not known eagerly to be waiting for them. What does he have to say? Pretty much that he doesn’t know anything about art but he knows what he likes. The truth of the matter, however, is that he pretty much likes what he knows, and what he knows is what he has heard smart scientists say. Were smart scientists to say that a form of yeast is intermediate between the great apes and human beings, Hitchens would, no doubt, conceive an increased respect for yeast. But that’s a journalist for you: all zeal and no content. No, no, not you, of course. You’re not like the others.
[Photo Credit: Turkey's First ID Conference, March 2007]
Bingo! That's exactly right, and it nicely punctures the sophistry offered up by theistic evolutionists.I agree with Jason. This is a fight between two Intelligent Design Creationists even though one of them (Ken Miller) pretends that he's not a creationist. What I like about this exchange is that Behe is honest and forthright about the implications of his belief in a designer. The Theistic Evolutionist Creationists on the other hand, aren't.
I usually tell students, keep QUIET. Act like a good little Darwinbot. Question nothing, no matter how ridiculous. Practice keeping a straight face. (Anyone who laughs will be disqualified.) Get great marks.It's called lying for Jesus.
A further hugely complicating factor is what we mean by the word "race". Populations in different parts of the world have clearly adapted to their environments in different ways. A trait that is beneficial in one environment may work against people in another. Obesity is a problem today because it once was beneficial to eat as much as one could while one could. Stratification - classifying people into categories of higher and lower status in a society - already occurs on the basis of weight just as it has on the basis of intelligence test scores.We all know what people mean when they talk about blacks and whites. Those are synonyms for Africans and Europeans. Unless Sternberg is being extremely pedantic, he's arguing that there are no such thing as distinct populations of Europeans and Africans that differ genetically. Races—or demes if you wish—don't exist according to him.
But there is nothing special about skin colour that serves as a basis for differentiating humans into so-called races. Skin colour correlates only weakly with genetic differentiations. Sarah Tishkoff, a geneticist at the University of Maryland, and Kidd have found that the genetic differences among black Africans are often greater than those between blacks and whites. The significance of those labels stems only from the fact that society has found it convenient to label races on the basis of skin colour.
Curiously, we do not apply the concept of "race" to colours of dogs or cats - or moths, for that matter. For some of these, colour can be important: being a black moth confers camouflage advantages in polluted environments and disadvantages in clean environments - and vice versa for white moths. Similarly, our ancestors in Africa were almost certainly dark-skinned because it provided better protection against the particular challenges of the environment, such as ultraviolet light. We could of course refer to moths as being of different "races". We do not, presumably because we are less interested in creating social classes for moths than for people.
The problems with our understanding of intelligence and race show that the criticism being levelled at Watson is based on science rather than political correctness. Intelligence is clearly a far more complicated issue than standard testing allows. And race is a socially constructed concept, not a biological one. It derives from people's desire to classify. Whether people with a genetic predisposition toward fatness will be classified as a separate race remains to be seen.
Menashe, I., Abaffy, T., Hasin, Y., Goshen, S., Yahalom, V., Luetje, C.W. and Lancet, D. (2007) Genetic Elucidation of Human Hyperosmia to Isovaleric Acid. PLoS Biology 5:e284 doi:10.1371/journal.pbio.0050284. [PLoS Biology]
"for their discovery of the mechanisms in the biological synthesis of ribonucleic acid and deoxyribonucleic acid"
Your Majesties, Your Royal Highnesses, Ladies and Gentlemen.
To maa man vaere hvis livet skal lykkes, «There must be two if life shall succeed», is the theme of a sentimental old Danish song. The author had in mind man and woman, but she probably did not know how right she was from a more elementary biological viewpoint. Two principles are necessary so that «life» shall «succeed». One consists of proteins, the other of nucleic acids. The analogy is more than just a play upon words. Just as man and woman are responsible for the regeneration of mankind, likewise is the interplay between proteins and nucleic acids the only, and universally repeated basic mechanism of life. In the long series of substances which build up viruses, bacteria, plants, and animals, everything else might vary, but the proteins and nucleic acids are always present as the life-supporting elements. These both show certain principal characteristics. Their molecules are very large, and are built up from thousands of smaller units linked together in chains - just like a string of pearls - which have a tendency to form helices. Single helices join together in complicated threads which can contain proteins or nucleic acids or both. In the mixed «super molecules», the reactions of life proceed in the subtle pattern of the intimately associated strands.
The proteins contain amino acids as their elementary part. In the whole of Nature on this earth, there are found only some twenty amino acids in proteins. The elementary parts of the nucleic acids, the nucleotides, consist of nitrogenous bases, sugar, and phosphoric acid. There are found in Nature practically no more than eight of these most important nucleotides, all of which contain phosphoric acid, but in which the nitrogenous base may be one of five different kinds. The sugar can be of two different kinds, one of which, «ribose», contains one more oxygen atom than the other, «deoxyribose». This seemingly insignificant difference in a single atom produces a remarkably great effect. Nucleic acids are divided into two different series because of this characteristic. These series have widely different functions, so widely different in fact, that this is the reason why we have two Prize Winners on the stage today.
«Deoxyribonucleic acids», which Arthur Kornberg has now synthesized, are mainly present as the hereditary substance in chromosomes. The «ribonucleic acids», which Severo Ochoa has synthesized, have other functions, such as to assist in the synthesis of proteins. The Swedish scientist Torbjörn Caspersson has played an important role in demonstrating this last fact. From his and other research-workers' discoveries, it has been possible to conclude that nucleic acids assist in the synthesis of protein. The exact chemical mechanism, however, is as yet unknown. Inasmuch as nucleic acids and proteins are the two main principles of life, it seemed highly probable that, vice versa, the proteins should take part in the rebuilding of nucleic acids. This seems so much the more probable when we realize that proteins, in the form of enzymes, take part in practically every chemical reaction in the biological world. It is to the everlasting credit of Ochoa and Kornberg to have clarified this fundamental mechanism by preparing proteins that build up nucleic acids in test tubes.
For proteins it has been proved, and for the nucleic acids it is highly probable, that the order of the different building blocks in the chains is by no means left to chance, but on the contrary is planned in detail for each kind of molecule and for each kind of living organism.
It is this regulated order between the building blocks that always makes human children grow up to be human beings, and the serpent's offspring grow up to be serpents. It is disturbances in this regulated order which change the hereditary factors and allows the variations of species over thousands of years. The almost infinite possibilities to combine the building blocks in different ways makes it possible to vary the form in which life appears on our earth. Let me give a comparable example. By different combinations of the 28 letters in our alphabet, we can write everything that can be expressed in our own language, as well as in all other languages. The building blocks of the proteins, the amino acids, are approximately equal in number to the letters of the alphabet. The protein molecules can be compared with words with 100, 1,000, or even 10,000 letters. It is clear that Nature here has been generous with the possibility to make different combinations amounting to astronomical figures. But here, another factor might be brought up. The differences between the amino acids are necessary not only to produce the possibilities for variation, but also to enable the proteins, by their enzymatic activity, to regulate the different aspects of metabolism. Even the two types of nucleic acids with 4 different nucleotides in each, when made up from 100 to 10,000 nucleotide units in each molecule, give a fantastic number of possible combinations. Thus it would seem as if it were too heroic an enterprise to try to find out the procedure whereby Nature forms such complicated substances as nucleic acids with such an unerring accuracy in placing each building block.
A few years ago, Ochoa and Kornberg, each in his own laboratory, started to investigate the problem. The development turned for Ochoa's part in a direction that made him work with systems that produced ribonucleic acids, while for Kornberg it led him to investigate the formation of deoxyribonucleic acids. They have both, in a series of outstanding investigations, without direct cooperation, but nevertheless, as personal friends probably profiting from each other's results, reached the goal at the same time. As everyone else, they were able to make use of results obtained by preceding research workers, among whom I can only mention a few. It might be of interest to mention that uric acid, the first representative of the purines (a class of nitrogenous bases that form part of the nucleic acids) was discovered in Sweden in 1776 simultaneously by both Carl Wilhelm Scheele and Torbern Bergman. It is a curious parallel to the shared Nobel Award of today, and a reminder of Sweden's great era in the science of chemistry. The German scientist Albrecht Kossel received the Nobel Prize in 1910 for his elucidation of the chemistry of the nitrogenous bases of the nucleic acids, whereas the English scientist Alexander Todd clarified in detail the chemical properties of the nucleic acids, and received the Nobel Prize for Chemistry in 1957. But what really enabled Ochoa and Kornberg to succeed was their own excellent previous work in related fields. Both have worked with bacteria from which they have made preparations of a high degree of purity, Ochoa from an acetic acid bacterium, and Kornberg from the coli bacterium. Ochoa's enzyme produces ribonucleic acids from ribonucleotides having twice the ratio of phosphoric acid residues as that contained in ribonucleic acid. The ribonucleic acid is formed by splitting out half of the phosphoric acid residues, and linking the nucleotides together to form large molecules, which, as far as we can prove today, do not differ in any way from natural nucleic acids. Kornberg's enzyme produces deoxyribonucleic acids in a similar, but not identical fashion. Both have arrived at the same, principally important result that in order to make the reaction start, it is necessary to add in the beginning a small amount of nucleic acid to act as a template. Otherwise the enzymes do not «know» which kind of nucleic acid they are to produce. As soon as they get a template to act as a guide, they start, just like a skilled type-setter, to copy the «manuscript» they have received. Here one recognizes life's own principle that like creates like. Even though several research workers had earlier suspected that such a mechanism was involved, the actual experimental proof is of greatest importance. Furthermore, Ochoa's enzyme has given us the possibility of enzymatically synthesizing simplified nucleic acids of great interest.
To give an idea of where the discoveries that are being honored today may lead to in the near future, I want to mention one example. Other scientists, especially S. S. Cohen in the U.S.A., have shown that the nucleic acid of a certain bacteriophage, T2, which is a kind of bacterial virus, contains a somewhat chemically different nitrogenous base. If bacteria are infected with T2 phage, this different nucleic acid is soon produced in the bacteria. Kornberg succeeded in explaining the mechanism in detail. T2 phage behaves like the worst kind of usurper. Within four minutes it produces a number of enzymes which destroy a nucleotide necessary for the bacterium's normal production of nucleic acids, and rebuilds it to the different nucleotide of the T2 phage, and thereby destroys the bacteria.
We are sure to witness in the near future several important discoveries in biochemistry, virus research, genetics, and cancer research as a consequence of the work of Ochoa and Kornberg. They have helped us to advance quite some distance on the road to understanding the mechanism of life.
Professor Severo Ochoa, Professor Arthur Kornberg, dear friends and colleagues. Some 130 years ago, Friedrich Wöhler, in the laboratory of Berzelius, synthesized urea from inorganic matter. This event occurred in the heart of this city of Stockholm, less than half a mile from where we are now standing. He thus overbridged the first gap between living and dead material. You have now made the second fundamental discovery on this pathway, the synthesis in test tubes of one of the two basic principles of life.
On behalf of the Caroline Institute, I extend to you our warm congratulations, and ask you to receive this year's Nobel Prize for Physiology or Medicine from the hands of His Majesty the King.
[©Laurence A. Moran and Pearson/Prentice Hall]
Horton, H.R., Moran, L.A., Scrimgeour, K.G., Perry, M.D. and Rawn, J.D. (2006) Principles of Biochemistry. Pearson/Prentice Hall, Upper Saddle River, NJ (USA)
Inorganic polyphosphate (poly P) is a chain of tens or many hundreds of phosphate (Pi) residues linked by high-energy phosphoanhydride bonds. Despite inorganic polyphosphate's ubiquity--found in every cell in nature and likely conserved from prebiotic times--this polymer has been given scant attention. Among the reasons for this neglect of poly P have been the lack of sensitive, definitive, and facile analytical methods to assess its concentration in biological sources and the consequent lack of demonstrably important physiological functions. This review focuses on recent advances made possible by the introduction of novel, enzymatically based assays. The isolation and ready availability of Escherichia coli polyphosphate kinase (PPK) that can convert poly P and ADP to ATP and of a yeast exopolyphosphatase that can hydrolyze poly P to Pi, provide highly specific, sensitive, and facile assays adaptable to a high-throughput format. Beyond the reagents afforded by the use of these enzymes, their genes, when identified, mutated, and overexpressed, have offered insights into the physiological functions of poly P. Most notably, studies in E. coli reveal large accumulations of poly P in cellular responses to deficiencies in an amino acid, Pi, or nitrogen or to the stresses of a nutrient downshift or high salt. The ppk mutant, lacking PPK and thus severely deficient in poly P, also fails to express RpoS (a sigma factor for RNA polymerase), the regulatory protein that governs > or = 50 genes responsible for stationary-phase adaptations to resist starvation, heat and oxidant stresses, UV irradiation, etc. Most dramatically, ppk mutants die after only a few days in stationary phase. The high degree of homology of the PPK sequence in many bacteria, including some of the major pathogenic species (e.g. Mycobacterium tuberculosis, Neisseria meningitidis, Helicobacter pylori, Vibrio cholerae, Salmonella typhimurium, Shigella flexneri, Pseudomonas aeruginosa, Bordetella pertussis, and Yersinia pestis), has prompted the knockout of their ppk gene to determine the dependence of virulence on poly P and the potential of PPK as a target for antimicrobial drugs. In yeast and mammalian cells, exo- and endopolyphosphatases have been identified and isolated, but little is known about the synthesis of poly P or its physiologic functions. Whether microbe or human, all species depend on adaptations in the stationary phase, which is truly a dynamic phase of life. Most research is focused on the early and reproductive phases of organisms, which are rather brief intervals of rapid growth. More attention needs to be given to the extensive period of maturity. Survival of microbial species depends on being able to manage in the stationary phase. In view of the universality and complexity of basic biochemical mechanisms, it would be surprising if some of the variety of poly P functions observed in microorganisms did not apply to aspects of human growth and development, to aging, and to the aberrations of disease. Of theoretical interest regarding poly P is its antiquity in prebiotic evolution, which along with its high energy and phosphate content, make it a plausible precursor to RNA, DNA, and proteins. Practical interest in poly P includes many industrial applications, among which is the microbial removal of Pi in aquatic environments.Much work has been done since this review was published in 1999 but the basic concepts haven't changed. Arthur Kornberg [Biochemist Arthur Kornberg (1918 - 2007)] was very interested in polyphosphates and he is responsible bringing it to the attention of the biochemistry community. His lab worked on polyphosphates for the past 25 years. As you know, Kornberg died last Friday but one of his papers on polyphosphate was just published two weeks ago (Zhang et al. 2007). That paper describes the enzyme polyphosphate kinase 1 in slime mold Dictyostelium discoideum, one of the few eukaryotes to have the enzyme that makes and degrades polyphosphate. The paper shows that polyphosphate regulates cell division in Dictyostelium.
Kornberg, A., Rao, N.N. and Ault-Riché, D. (1999) Inorganic polyphosphate: a molecule of many functions. Annu. Rev. Biochem. 68:89-125. [PubMed]
Li, L., Rao, N.N. and Kornberg, A. (2007) Inorganic polyphosphate essential for lytic growth of phages P1 and fd. Proc. Natl. Acad. Sci. (USA) 104(6):1794-1799. [PubMed]
Zhang, H., Gómez-García, M.R., Shi, X., Rao, N.N. and Kornberg, A. (2007) Polyphosphate kinase 1, a conserved bacterial enzyme, in a eukaryote, Dictyostelium discoideum, with a role in cytokinesis. Proc. Natl. Acad. Sci. (USA) 104:16486-16491. [PNAS] [PubMed]