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 of Mus musculus castaneus and Mus musculus musculus: populations with high and low N_e respectively. Our results revealed that the difference between π_N/π_S estimated for genes with high and low expression levels was significantly smaller for M. m. musculus compared to that observed for M. m. castaneus The difference between the π_N/π_S of broadly expressed and tissue specific genes was much higher for M. m. castaneus compared to that of M. m. musculus. Furthermore, the difference between the π_N/π_S computed for essential and non-essential genes was much smaller for M. m. musculus than M. 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 small N_e due to increased genetic drift.