UNSTABLE ALLELE OF THE AM-LOCUS OF NEUROSPORA-CRASSA

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  • 1 January 1979
    • journal article
    • research article
    • Vol. 93  (3) , 577-586
Abstract
The mutant strain am126 was isolated, using the direct selection procedure, after nitrous acid mutagenesis. It produced neither measurable NADP-dependent glutamate dehydrogenase (GDH) nor immunologically cross-reacting material. That the am126 strain produced some form of GDH product was shown by the fact that it complemented several other am mutant strains. The GDH formed by complementation between am126 and each of 2 other am mutants was relatively thermolabile, but could not be distinguished from wild-type GDH by electrophoresis in polyacrylamide gels. This, together with the relatively high yield of the complementation enzymes, suggests that the am126 product is a polypeptide chain not grossly abnormal in structure. The spontaneous revertant frequency was 0.3-3 prototrophic revertants/105 live cells. This frequency was at least 40 times greater than that for am19, which had the 2nd highest spontaneous revertant frequency among the mutants tested. Neither meiosis nor mutagenesis increased the revertant frequency, nor did incubation at elevated temperatures lower it. Sixty-eight revertant strains were examined for thermostability of their GHD. All apparently were identical to wild type. Seven of the revertant strains were also tested for instability with regard to forward mutation to am auxotrophy. None was unstable. Models for the genetic instability of the am126 mutation are discussed.