isolation of MMS - and histidine-sensitive mutants in Neurospora crassa

A simple method of replica plating has been used to isolate mutants of Neurospora crassa that have increased sensitivity to methyl methanesulfonate (MMS) and/or to histidine. Twelve mutants with increased sensitivity to MMS and one mutant with increased sensitivity to histidine showed Mendelian segregation of the mutant phenotypes. Three mutants were mapped to loci not previously associated with MMS sensitivity. Two other were allelic to the UV- and MMS-sensitive mutant, mei-3. Survival curves indicate that conidia (mutant or wild-type) survive on much higher concentrations of MMS at 25 degrees than at 37 degrees. In contrast, mycelial growth is more resistant to MMS at 37 degrees. The possibility of qualitatively different repair processes at these two temperatures is discussed.