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Number of proteins expressed in cell - (Apr/29/2010 )


Does anyone know how many different proteins are expressed in a mammalian cell?
I know there is supposed to be between 10 - 20 thousand but can anyone give me a reference for this?
Has there been a proteomic study done to answer this question?


I guess that you can look at the genome and use the number of genes found as an estimate of the number of proteins expressed. However, not all cells will express all genes and there are things like expressed pseudogenes that complicate things a bit.


Although the DNA genome that is within the nucleus of each human cell is estimated to encode for >30,000 proteins, only a fraction of these proteins are expressed in each cell type and it is this differential level of protein expression which largely accounts for the difference between, for instance, a skin cell versus a liver cell. Within a given cell different proteins vary widely in their level of expression - with some regulatory proteins being present in perhaps only a few copies while other proteins (e.g. those found in muscles) may be present in as many as millions of copies/cell.

From Background Information on the Human Proteome and the Yale/NHLBI Proteomics Center.

The fact is, we just don't know how many proteins comprise the human proteome -- a project to find out was started last year (see here).