Biochemical genetics of Neurospora nuclease II: Mutagen sensitivity and other characteristics of the nuclease mutants

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Abstract
SUMMARY: Five newnucmutants ofNeurospora crassawere characterized for their relative sensitivities to different mutagens (UV, MNG, MMS), to mitomycin-C and to histidine; latter has been shown to inhibit the growth of certain UV sensitive mutants. These mutants were also compared for their capabilities for spontaneous mutation as determined by resistance to p-fluoro-phenylalanine. Based on these characterization, the mutants seem to belong to two groups. The first group includednuc-3andnuc-6which showed sensitivity to all mutagen tested and possessed capability for a very high frequency of spontaneous mutation (i.e. mutator effect). The second group includednuc-4, nuc-5andnuc-7; these were as resistant to different mutagens as the wild type strain, but possessed an antimutator effect (i.e. the frequency of spontaneous mutation by these three mutants were at least 0·5–100 × less than the wild type strains). There was some variation in these properties of mutants belonging to the two groups. Among all the fivenucmutants,nuc-3was characterized by extreme sensitivity to all mutagens. None of the fivenucmutants were sensitive to histidine. The properties ofnucmutants are discussed in relation to their possible role in DNA repair and recombination.

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