PHYLOGENY AND EVOLUTIONARY RATES OF G-PROTEIN ALPHA-SUBUNIT GENES

Rooted phylogenetic trees for a total of 34 genes encoding the stimulatory (s-alpha), inhibitory (i-alpha), transducin (t-alpha), G(x) (x-alpha), G(z) (z-alpha), G11 (alpha-11), G12 (alpha-12), G13 (alpha-13), G16 (alpha-16), G(q) (q-alpha), and other (o-alpha) G protein alpha-subunits have been constructed. The analysis shows that the G12 (alpha-12 and alpha-13), G(q) (alpha-11, alpha-16, and q-alpha), and G(s) (s-alpha genes) groups form one cluster, and the G(x) (x-alpha and z-alpha genes), G(i) (i-alpha genes), G(t) (t-alpha-1 and t-alpha-2), and G(o) (o-alpha genes) groups form another cluster. During mammalian evolution, the rates of synonymous substitutions for these genes were estimated to be between 1.77 x 10(-9)/site/year and 5.63 x 10(-9)/site/year, whereas those of nonsynonymous substitutions were between 0.008 x 10(-9)/site/year and 0.067 x 10(-9)/site/year. These evolutionary rates are similar to those for histone genes, suggesting equally important biological functions of the G protein alpha-subunits.