CONSERVED REGIONS OF THE TIMELESS (TIM) CLOCK GENE IN DROSOPHILA ANALYZED THROUGH PHYLOGENETIC AND FUNCTIONAL-STUDIES

Circadian (similar to 24-hr) rhythms in Drosophila melanogaster depend upon cyclic expression of the period (per) and timeless (tim) genes, which encode interacting components of the endogenous clock. The per g ene has been isolated from other insects and, more recently a per orth olog was found in mammals where its expression oscillates in a circadi an fashion. We report here the complete sequence of a tim gene from an other species, Drosophila virilis. TIM is better conserved than the PE R protein is between these two species (76 vs. 54% overall amino acid identity), and putative functional domains, such as the PER interactio n domains and the nuclear localization signal, are highly conserved. T he acidic domain and the cytoplasmic localization domain, however, are within the least conserved regions. In addition, the initiating methi onine in the D. virilis gene lies downstream of the proposed translati on start for the original D. melanogaster tim cDNA and corresponds to the one used by D. simulans and D. yakuba. Among the most conserved pa rts of TIM is a region of unknown function near the N terminus. We sho w here that deletion of a 32 amino acid segment within this region aff ects rescue of rhythms in arrhythmic tim(01) flies. Flies carrying a f ull-length tim transgene displayed rhythms with similar to 24-hr perio ds, indicating that a fully functional clock can be restored in tim(01 ) flies through expression of a tim transgene. Deletion of the segment mentioned above resulted in very long activity rhythms dth periods ra nging front 30.5 to 48 hr.