Effect of genetic drift on determinants of protein evolution

A number of previous studies reported that gene expression, tissue specificity, gene essentiality and the number of protein–protein interactions influence the rate of protein evolution. Here we investigated the influence of effective population size (N e ) on these determinants of protein evolution. For this purpose, we compared the ratio of non-synonymous-to-synonymous diversities (π N /π S ) estimated for protein-coding genes ofMus musculus castaneus andMus musculus musculus : populations with high and lowN e respectively. Our results revealed that the difference betweenπ N /π S estimated for genes with high and low expression levels was significantly smaller forM. m. musculus compared to that observed forM. m. castaneus . The difference between theπ N /π S of broadly expressed and tissue specific genes was much higher forM. m. castaneus compared to that ofM. m. musculus. Furthermore, the difference between theπ N /π S computed for essential and non-essential genes was much smaller forM. m. musculus thanM. m. castaneus . A similar pattern was observed for genes involved in many protein–protein interactions versus those involved in one. These results suggest that the effects of the determinants on protein evolution were much reduced for the population with smallN e due to increased genetic drift.