The correct version of the Central Dogma of Molecular Biology is .... [see Basic Concepts: The Central Dogma of Molecular Biology]
... once (sequential) information has passed into protein it cannot get out again (F.H.C. Crick, 1958)Eugene Koonin has an article in Biology Direct entitled Does the central dogma still stand (Koonin, 2012).
The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred from protein to either protein or nucleic acid. (F.H.C. Crick, 1970)
There are very few firm principles in biology. It is often said, in one form or another, that the only actual rule is that there are no rules, i.e. exceptions can be found to every "fundamental‟ principle if one looks hard enough. The principle known as the Central Dogma of molecular biology seems to be an exception to this "ubiquitous exception‟ rule. The Central Dogma was conjured by Francis Crick in response to the discovery of reverse transcription, when it became clear that the RNA to DNA information transfer was an integral part of the life cycle of retro-transcribing genetic elements (subsequent developments demonstrated the broad occurrence of reverse transcription in cells). Crick realized that, all its biologically fundamental implications notwithstanding, reverse transcription was essentially business as usual, i.e. interconversion of different forms of nucleic acids on the basis of universal rules of base complementarity. The central dogma places the actual „exclusion principle‟ at another stage of biological information transfer, translation. Thus, "There is no information transfer from protein to nucleic acid‟, postulates the Central Dogma.Koonin goes on to argue that prions violate the Central Dogma. Prions are an example of proteins that can have multiple conformations and the transition from one conformation to another is often cooperative. Thus, if one protein changes conformation, it can trigger changes in hundreds of others.
Some prion-like proteins affect translation or transcription or even chromatin conformation. In some cases the transformation in conformation is triggered by stress so that under some specific conditions the prion-like protein senses the trigger and modifies nucleic acid. According to Koonin ...
Thus, the Central Dogma of molecular biology is invalid as an "absolute‟ principle: transfer of information from proteins (and specifically from protein sequences) to the genome does exist. This is not to deny that the Central Dogma does capture the principal route of information transfer in biology: the main flow information does follow the path in Figure 1, and elaborate mechanisms ensuring acceptable fidelity operate on each step. And, there is a major discontinuity between the levels of RNA and protein because during translation because the coupling of amino acids with the cognate tRNAs does not involve direct recognition but rather requires dedicated enzymes, aminoacyl-tRNA synthetases, that recognize and connect the partners. The opposite direction of information flow, from proteins to the genome, is asymmetrical (not a simple reversion), much more modest quantitatively and intrinsically stochastic but nevertheless appears to be important in evolution.This is largely a question of how you define information flow. In Crick's original version of the Central Dogma he was quite obviously talking about the flow of genetic information as specified in the sequence of bases in DNA (sequential information). In that sense the Central Dogma would only be refuted by demonstrating reverse translation.
Proteins that modify DNA or RNA have been known for 35 years. I don't think they count as violations of the Central Dogma even if their activity is influenced by the environment. However, if people like Eugene Koonin are so bothered by the Central Dogma that they want to quibble over issues like this then maybe we should stop talking about it altogether. The Central Dogma may have outlived its usefulness. (At least one textbook—Berg, Tymoczko, and Stryer—has dropped it.)
Koonin, E. (2012) Does the central dogma still stand? Biology Direct 1:27 [doi: 10.1186/1745-6150-7-27] [Biology Direct Abstract]