REGULATORY MUTANTS AT THE his1 LOCUS OF YEAST

[摘要] The hisl gene in Saccharomyces cereuisiae codes for phosphoribosyl transferase, an allosteric enzyme that catalyzes the initial step in histidine biosynthesis. Mutants that specifically alter the feedback regulatory function were isolated by selecting hisl prototrophic revertants that overproduce and excrete histidine. The prototrophs were obtained from diploids homoallelic for his1-7 and heterozygous for the flanking markers thr3 and arg6 . Among six independently derived mutant isolates, three distinct levels of histidine excretion were detected. The mutants were shown to be second-site alterations mapping at the his1 locus by recovery of the original auoxtrophic parental alleles. The double mutants, HIS1-7e , are dominant with respect to catalytic function but recessive in regulatory function. When removed from this hisl-7 background, the mutant regulatory site ( HIS1-e ) still confers prototrophy but not histidine excretion. To yield the excretion phenotype, the primary and altered secondary sites are required in cis array. Differences in histidine excretion levels correlate with resistance to the histidine analogue, triazoalanine.

[学科分类] 医学（综合）