EVOLUTION OF TRANSCRIPTION-REGULATING PROTEINS BY ENZYME RECRUITMENT - MOLECULAR-MODELS FOR NITROGEN METABOLITE REPRESSION AND ETHANOL UTILIZATION IN EUKARYOTES

Studies on the quinic acid utilisation gene (clot) cluster in Aspergil lus nidulans showed that the genes encoding transcriptional activator and repressor proteins evolved by co-opting duplicated copies of genes encoding metabolic enzymes. In order to test the hypothesis that this was a general route for the genesis of regulatory proteins, the origi ns of the major control protein mediating nitrogen metabolite repressi on (an example of inter-pathway regulation) and ethanol utilisation (a n example of intra-pathway regulation) in filamentous fungi were sough t. The regulatory proteins mediating nitrogen metabolite repression we re deduced to have originated in a duplication of genes encoding the a nthranilate synthase complex which is active in the shikimate pathway. The major protein regulating ethanol utilisation was deduced to have its origin in the fusion of duplicated genes encoding the aldehyde and alcohol dehydrogenases (ALDA and ALCA). These data strongly support t he view that transcriptional regulatory proteins evolve by the recruit ment of functional domains provided by metabolic enzymes.