CLONING AND CHARACTERIZATION OF THE ADENINE PHOSPHORIBOSYLTRANSFERASE-ENCODING GENE (APT1) FROM SACCHAROMYCES-CEREVISIAE

We have cloned, sequenced and characterized the APT1 (adenine phosphor ibosyltransferase) gene from Saccharomyces cerevisiae. The APT1 sequen ce includes and open reading frame encoding 221 amino acids is contain ed within a 1322-bp insert that complements APRT-deficient mutants to wild-type levels of enzyme activity. Analysis by primer extension reve aled multiple transcription start points (tsp) and a major tsp 21-bp u pstream from the ATG start codon. A transcript initiated at the major tsp would yield a 700-nt mRNA which is in agreement with the size obse rved by Northern analysis. Sequence comparison indicates that the yeas t enzyme shares strong similarities with other known APRT of bacterial , invertebrate, plant and mammalian origins.