Isolation, characterization, and inactivation of the APA1 gene encoding yeast diadenosine 5',5'''-P1,P4-tetraphosphate phosphorylase.

The gene encoding diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) phosphorylase from yeast was isolated from a lambda gt11 library. The DNA sequence of the coding region was determined, and more than 90% of the deduced amino acid sequence was confirmed by peptide sequencing. The Ap4A phosphorylase gene (APA1) is unique in the yeast genome. Disruption experiments with this gene, first, supported the conclusion that, in vivo, Ap4A phosphorylase catabolizes the Ap4N nucleotides (where N is A, C, G, or U) and second, revealed the occurrence of a second Ap4A phosphorylase activity in yeast cells. Finally, evidence is provided that the APA1 gene product is responsible for most of the ADP sulfurylase activity in yeast extracts.