ACCELERATED EVOLUTION OF CYTOCHROME-B IN SIMIAN PRIMATES - ADAPTIVE EVOLUTION IN CONCERT WITH OTHER MITOCHONDRIAL PROTEINS

We have sequenced the cytochrome b gene of Horsfield's tarsier, Tarsiu s bancanus, to complete a data set of sequences for this gene from rep resentatives of each primate infraorder. These primate cytochrome b se quences were combined with those from representatives of three other m ammalian orders (cat, whale, and rat) in an analysis of relative evolu tionary rates. The nonsynonymous nucleotide substitution rate of the c ytochrome b gene has increased approximately twofold along lineages le ading to simian primates compared to that of the tarsier and other pri mate and nonprimate mammalian species. However, the rate of transversi onal substitutions at fourfold degenerate sites has remained uniform a mong all lineages. This increase in the evolutionary rate of cytochrom e b is similar in character and magnitude to that described previously for the cytochrome c oxidase subunit II gene. We propose that the evo lutionary rate increase observed for cytochrome b and cytochrome c oxi dase subunit LI may underlie an episode of coadaptive evolution of the se two proteins in the mitochondria of simian primates.