Isolation of circadian clock mutants of Neurospora crassa.

Three mutants of Neurospora crassa have been isolated which have altered period lengths of their circadian rhythm of conidiation. The strains, designated "frequency" (frq), were obtained after mutagenesis of the band (bd) strain with N-methyl-N'-nitro-N-nitrosoguanidine. In continuous darkness at 25 degrees bd has a period length of 21.6 +/- 0.5 hours; under the same conditions the period length of frq-1 is 16.5 +/- 0.5 hours; frq-2, 19.3 +/- 0.4 hours; and frq-3, 24.0 +/- 0.4 hours. Each of the mutants segregates as a single nuclear gene. All three mutants appear very tightly linked to each other, but it has not yet been determined whether the mutants are allelic. No major changes in the responses to light and temperature have been observed in any of the mutants. It is suggested that these mutants represent alterations in the basic timing mechanism of the circadian clock of Neurospora.