Humans have about 25,000 genes. About 20,000 of these genes are protein-coding genes.1 That means, of course, that humans make at least 20,000 proteins. Not all of them are different since the number of protein-coding genes includes many duplicated genes and gene families. We would like to know how many different proteins there are in the human proteome.
The latest issue of Science contains an insert with a chart of the human proteome produced by The Human Protein Atlas. Publication was timed to correspond with release of a new version of the Cell Atlas at the American Society of Cell Biology meeting in San Francisco. The Cell Atlas maps the location of about 12,000 proteins in various tissues and organs. Mapping is done primarily by looking at whether or not a gene is transcribed in a given tissue.A total of 7367 genes (60%) are expressed in all tissues. These "housekeeping" genes correspond to the major metabolic pathways and the gene expression pathway (e.g. RNA polymerase subunits, ribosomal proteins, DNA replication proteins). Most of the remaining genes are tissue-specific or developmentally specific.