Temperature Compensation of Circadian Period Length in Clock Mutants of Neurospora crassa.

Temperature compensation of circadian period length in 12 clock mutants of Neurospora crassa has been examined at temperatures between 16 and 34 degrees C. In the wild-type strain, below 30 degrees C (the "breakpoint" temperature), the clock is well-compensated (Q(10) = 1), while above 30 degrees C, the clock is less well-compensated (Q(10) = 1.3). For mutants at the frq locus, mutations that shorten the circadian period length (frq-1, frq-2, frq-4, and frq-6) do not alter this temperature compensation response. In long period frq mutants (frq-3, frq-7, frq-8), however, the breakpoint temperature is lowered, and the longer the period length of the mutants the lower the breakpoint temperature. Long period mutants at other loci exhibit other types of alterations in temperature compensation-e.g. chr is well-compensated even above 30 degrees C, while prd-3 has a Q(10) significantly less than 1 below 30 degrees C. Prd-4, a short period mutant, has several breakpoint temperatures. Among four double mutants examined, the only unusual interaction between the individual mutations occurred with chr prd, which had an unusually low Q(10) value of 0.86 below 27 degrees C. There was no correlation between circadian period length and growth rate. These strains should be useful tools to test models for the temperature compensation mechanism.