The tim Mutant of the Drosophila Rhythm Gene timeless Manifests Allele-Specific Interactions with period Gene Mutants

eliminates per mRNA cycling in the eye in an otherwise To identify new components of the Drosophila circawild-type fly (Zeng et al., 1994). PER is a nuclear protein dian clock, we screened chemically mutagenized flies and enters the nuclei of lateral neurons, putative pacefor suppressors or enhancers of the long periods charmaker cells in the brain (Liu et al., 1992; Zerr et al., 1990; acteristic of the period (per) mutant allele perL. We Ewer et al., 1992; Frisch et al., 1994), at a specific time isolated a novel mutant that maps to the rhythm gene of day (Curtin et al., 1995; Lee et al., 1996), and this timeless (tim). This novel allele, timSL, alters the tempoentry is altered in per L mutant flies (Curtin et al., 1995). ral pattern of per L protein nuclear localization and reMore recently, it has been shown that a change in the stores temperature compensation to perL flies. timSL PER phosphorylation pattern is a very early biochemical more generally manifests specific interactions with change detected immediately after a light pulse (Lee et different per alleles. The identification of this first al., 1996). period-altering tim allele provides further evidence In the fly, PER is in a heterodimeric complex with the that TIM is a major component of the clock, and the tim gene product (TIM), which also can enter the nucleus allele-specific interactions with PER provide evidence (Zeng et al., 1996; Lee et al., 1996; Hunter-Ensor et al., that the PER/TIM heterodimer is a unit of circadian 1996; Myers et al., 1996). Both tim mRNA and TIM cycle function. Although timSL fails to restore PER-L/TIM inabundance(Sehgalet al., 1995;Zenget al., 1996;Huntertemperature insensitivity in yeast, it alters the TIM Ensor et al., 1996; Myers et al., 1996), and the TIM phosphosphorylation pattern during the late night. The efphorylationstate alsochangeswith time (Zeng et al., 1996). fects on phosphorylation suggest that timSL functions There is one reported tim mutation, tim (Sehgal et al., as a partial bypass suppressor of perL and provide 1994), which is a null mutant with no protein (Myers et al., evidence that the TIM phosphorylation program con1995, 1996; Hunter-Ensor et al., 1996; Zeng et al., 1996). tributes to the circadian timekeeping mechanism. Neither per nor tim mRNA cycles in this mutant (Sehgal