APT1, but not APT2, codes for a functional adenine phosphoribosyltransferase in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae has two separate genes (APT1 and APT2) t hat encode two potentially different forms of adenine phosphoribosyltransfe rase (APRT). However, genetic analysis indicated that only APT1 could code for a complementing activity. Cloning and expression of both the APT1 and A PT2 genes in Escherichia coli showed that although discrete proteins (APRT1 and APRT2) were made by these genes, only APRT1 had detectable APRT activi ty. Northern and Western blot analyses demonstrated that only APT1 was tran scribed and translated under normal physiological conditions in yeast. Phyl ogenetic analysis revealed that APRT1 and APRT2 are evolutionary closely re lated and that they arise from a gene duplication event. We conclude that A PT1 is the functional gene in S. cerevisiae and that APT2 is a pseudogene.