Novel interallelic complementation at the his1 locus of yeast.

In yeast, 17 histidine-requiring mutants derived from and interallelically complementary to his1-7 were analyzed. The genetic basis of the complementation response was elucidated by mitotic and meiotic gene conversion. Each allele probably carries an unaltered 7-site mutation and a unique second-site alteration. The second-site alterations appear to be clustered within the proximal and distal segments of the his1 structural gene. Models of intraalelic complementation are reviewed in light of the unique complementational response between a single-site mutant and a double mutant including the identical altered base sequence.