Title: Genetic analysis of purple adenine (ad-3) mutants induced by methyl methanesulfonate in Neurospora crassa
Abstract: Abstract The mutagenicity of methyl methanesulfonate (MMS) was studied in a genetically marked two-component heterokaryon of Neurospora crassa . Types of genetic alterations detectable in this system are ( I ) point mutations in the ad -3 A and ad -3 B loci; ( 2 ) multilocus (chromosome) deletions in the ad -3 region, and ( 3 ) recessive lethal mutations in the whole genome. Study of the inactivation kinetics of the heterokaryotic and homokaryotic conidial fractions has made it possible to distinguish between nuclear and cytoplasmic inactivation. Forward mutations in the ad -3 region induced by MMS in the heterokaryotic fraction of conidia were obtained by a direct method with the following results: ( I ) The overall ad -3 forward mutation frequency increases in proportion to the 1.91 power of the concentration of MMS. ( 2 ) The forward mutation frequency of point mutations at the ad -3 A and ad -3 B loci increases in proportion to the 1.68 power of the concentration. ( 3 ) The forward mutation frequency of chromosome deletions in the ad -3 region increases more than exponentially with increasing concentrations of MMS. ( 4 ) After treatment for 300 min with 20 m M MMS, 15.5% of the ad -3 mutations are multilocus deletions. Tests for genotype and allelic complementation of the point mutations showed that ( I ) the ratio between ad -3 B and ad -3 A mutants was 1.75, ( 2 ) 52.1% of the ad -3 B mutants showed allelic complementation, with 39.2% non-polarized and 12.9% polarized complementation patterns and 47.9% noncomplementing mutants, and ( 3 ) both the ratio between point mutations in the ad -3 A and ad -3 B loci and the spectrum of complementation patterns among the ad -3 B mutants were independent of MMS concentration.
Publication Year: 1973
Publication Date: 1973-04-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 21
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