PRS5, THE 5TH MEMBER OF THE PHOSPHORIBOSYL PYROPHOSPHATE SYNTHETASE GENE FAMILY IN SACCHAROMYCES-CEREVISIAE, IS ESSENTIAL FOR CELL VIABILITY IN THE ABSENCE OF EITHER PRS1 OR PRS3

In Saccharomyces cervisiae, an open reading frame, YOL061w, encodes a polypeptide with sequence similarity to the four known 5-phosphoribosy l-1(alpha)-pyrophosphate synthetase (PRS) genes since it contains a di valent cation binding site and a phosphoribosyl pyrophosphate binding site. We regard YOL061w as the fifth member of the PRS gene family, PR S5, Loss of Prs5p has a significant impact on PRS Enzyme activity, cau sing it to be reduced by 84%. On the other hand, Delta prs5 strains ar e not affected in growth or in the size of their nucleotide pools. How ever, simultaneous deletion of PRS1 and PRS5 or PRS3 and PRS5 rendered the strains inviable, which implies that PRS5 plays an important role in the maintenance of PRS function in S. cerevisiae.