Comparative Analyses of Homocitrate Synthase Genes of Ascomycetous Yeasts

Most ascomycetous yeasts have 2 homocitrate synthases (HCSs). Among the fungal lysine biosynthesis-related genes, only the HCS gene was duplicated in the course of evolution. It was recently reported that HCS of Saccharomyces cerevisiae has an additional function in nuclear activities involving chromatin regulation related to DNA damage repair, which is not related to lysine biosynthesis. Thus, it is possible that the bifunctionality is associated with HCS gene duplication. Phylogenetic analysis showed that duplication has occurred multiple times during evolution of the ascomycetous yeasts. It is likely that the HCS gene duplication in S. cerevisiae occurred in the course of Saccharomyces evolution. Although the nucleosome position profiles of the two S. cerevisiae HCS genes were similar in the coding regions, they were different in the promoter regions, suggesting that they are subject to different regulatory controls. S. cerevisiae has maintained HCS activity for lysine biosynthesis and has obtained bifunctionality.