Allelic variability in comparative complementation confirming that the ade12-specified protein of yeast is bifunctional.

Mutants at the adel2 locus of Saccharomyces cerevisiae are deficient in adenylosuccinate synthetase and are also responsible for constitutive purine biosynthetic activity. Ninety-six alleles were tested for restoration of each of these functions by allelic complementation and the results from the two types of test of every allele pair in the two matrices were compared with each other. Either the reactions were consistent, both complementing or noncomplementing, or inconsistent, with either enzymatic or regulatory function restored. The frequency and distribution of inconsistent behavior accords with the expectation that the adel2 locus specifies a bifunctional protein serving independent roles in enzymatic activity and in regulation of pathway activity. In a parallel experiment and analysis the addition of 1.0 m KCl increases the overall frequency of positive complementation, but skews the distribution of inconsistency sharply toward restoration of the regulatory function.