Complementation relationships ofNeurospora ammutants in relation to their formation of abnormal varieties of glutamate dehydrogenase

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Abstract
Six newammutants ofNeurospora,am14–am19, with defective formation of NADP-linked glutamate dehydrogenase, were isolated following treatment of conidia with nitrous acid. This brings the number of genetically distinct and viableammutants to sixteen. Heterocaryon-compatible isolates of each of the new mutants were tested for complementation with each of the mutants previously known. A number of new complementary combinations were found which add to the complexity of the complementation map which, however, remains linear.The mutants which show complementation aream1,am2,am3,am7,am14andam19. It has proved possible to isolate an altered form of glutamate dehydrogenase from each of these exceptam14, which appears to produce no protein fractionating like the normal enzyme. Among the non-complementing mutants,am4produces an easily-isolated inactive form of glutamate dehydrogenase. These results agree with the immunochemical findings of Roberts & Pateman (1964).Of the mutationally altered forms of the enzyme, theam1,am2,am3andam7varieties are electrophoretically identical or closely similar to the normal protein, while theam4andam19varieties move faster towards the anode at pH 8·5,am19being the faster of the two. Theam19protein, like theam2andam3proteins previously reported on, can be activated to give some enzyme activity, but the activity obtained is much lower for this mutant than foram2oram3.All the complementary pairs of mutants, including those involvingam19, form active enzyme varieties which have very close to normal electrophoretic properties. In several cases the complementation enzyme is less stable to heat than the wild-type enzyme.