INTERMITTENT DIVERGENCE OF THE PROTEIN-TYROSINE KINASE FAMILY DURING ANIMAL EVOLUTION

The protein tyrosine kinases (PTKs) are a large protein family consist ing of many subfamilies with a variety of domain structures, The basic functions are thought to differ for different subfamilies. To know th e dates at which the subfamilies diverged by gene duplications, a phyl ogenetic tree of the PTKs was inferred by comparing sequences from a n ide range of species covering diploblasts and triploblasts. The PTK tr ee revealed that almost all of the gene duplications that gave rise to different subfamilies occurred rapidly before the diploblast-triplobl ast split, accompanying with rapid amino acid substitutions, This type of gene duplication was, however, rarely observed after that split, L ong after the subfamily divergence, another type of gene duplication t hat gave rise to diverse tissue-specific genes occurred in each subfam ily on the chordate lineage since the separation from arthropods, This type of gene duplication occurred frequently before the fish-tetrapod split, accompanying with rapid amino acid substitutions, In contrast, both the frequency of gene duplications and the rate of the amino aci d substitutions were considerably reduced after that split, These resu lts strongly suggest that the PTKs diverged intermittently, but not gr adually, during animal evolution. (C) 1997 Federation of European Bioc hemical Societies.