ISOLATION AND CHARACTERIZATION OF A TEMPERATURE-SENSITIVE CIRCADIAN CLOCK MUTANT OF NEUROSPORA-CRASSA

A new circadian clock mutant has been isolated in Neurospora crassa. T his new mutation, called period-6 (prd-6), has two features novel to k nown clock mutations. First, the mutation is temperature sensitive. At restrictive temperatures (above 21 degrees) the mutation shortens cir cadian period length from a wild-type value of 21.5 hr to 18 hr. At pe rmissive temperatures (below 21 degrees) the mutant has a 20.5-hr peri od length close to that of the wild-type strain. Second, the prd-6 mut ation is epistatic to the previously isolated clock mutation period-2 (prd-2). This epistasis is unusual in that the prd-2 prd-6 double muta nt strain has an 18-hr period length at both the restrictive and permi ssive temperatures. That is, the temperature sensitive aspect of the p henotype of the prd-6 strain is lost in the prd-2 prd-6 double mutant strain. This suggests that the gene products of the prd-2 and prd-6 lo ci mw interact physically and that the presence of a normal prd(2+) pr otein is required for low temperature to ''rescue'' the prd-6 mutant p henotype. These results, combined with our recent finding that prd-2 a nd some alleles of the frq gene show genetic synergy, suggest that it may be possible to establish a more comprehensive model of the Neurosp ora circadian clock.