Genomic Exploration of the Hemiascomycetous Yeasts: 21. Comparative functional classification of genes

We explored the biological diversity of hemiascomycetous yeasts using a set of 22 000 newly identified genes in 13 species through BLASTX searches. Ge nes without clear homologue in Saccharomyces cervisiae appeared to be conse rved in several species, suggesting that they were recently lost by S. cerv isiae. They often identified well-known species-specific traits. Cases of g ene acquisition through horizontal transfer appeared to occur very rarely i f at all. All identified genes were ascribed to functional classes. Functio nal classes were differently represented among species. Species classificat ion by functional clustering roughly paralleled rDNA phylogeny, Unequal dis tribution of rapidly evolving, ascomycete-specific, genes among species and functions was shown to contribute strongly to this clustering. A few cases of gene family amplification were documented, but no general correlation c ould be observed between functional differentiation of yeast species and va riations of gene family sizes. Yeast biological diversity seems thus to res ult from limited species-specific gene losses or duplications, and for a la rge part from rapid evolution of genes and regulatory factors dedicated to specific functions. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.