CIRCADIAN RHYTHMS IN NEUROSPORA CRASSA: INTERACTIONS BETWEEN CLOCK MUTATIONS

Patricia L. Lakin-Thomas ¹ and Stuart Brody ¹

¹ Department of Biology, University of California at San Diego, La Jolla, California, 92093

Mutations at four loci in Neurospora crassa that alter the period of the circadian rhythm have been used to construct a series of double mutant strains in order to detect interactions between these mutations. Strains carrying mutations at three of these loci have altered periods on minimal media: prd-1, several alleles at the oli^r (oligomycin resistance) locus and four alleles at the frq locus. A mutation at the fourth locus, cel, which results in a defect in fatty acid synthesis, also leads to lengthening of the period when the medium is supplemented with linoleic acid (18:2). The cel mutation was crossed into strains carrying the frq, prd-1 and oli^r mutations, and the periods of the double mutant strains with and without 18:2 supplementation were determined. In addition, data from the literature for other combinations of loci and/or chemical effects on the period have been reanalyzed.—It was found that (1) both prd-1 and oli^r are epistatic to the effects of 18:2 on cel; (2) in the series of cel frq double mutant strains, the period-lengthening effect of 18:2 is inversely proportional to the period of the frq parent, indicating an interaction between frq and cel; (3) period effects reported in the literature can be described as changes by a fixed ratio or percentage of the period rather than by a fixed number of hours, and the data, therefore, can support a multiplicative as well as an additive model.—Several biochemical interpretations of these interactions are discussed, based on simple chemical kinetics, enzyme inhibition kinetics and the control of flux through metabolic pathways.

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