Isolation and analysis of six timeless alleles that cause short- or long-period circadian rhythms in Drosophila.

In genetic screens for Drosophila mutations affecting circadian locomotion rhythms, we have isolated six new alleles of the timeless (tim) gene. Two of these mutations cause short-period rhythms of 21-22 hr in constant darkness, and four result in long-period cycles of 26-28 hr. All alleles are semidominant. Studies of the genetic interactions of some of the tim alleles with period-altering period (per) mutations indicate that these interactions are close to multiplicative; a given allele changes the period length of the genetic background by a fixed percentage, rather than by a fixed number of hours. The tim(L1) allele was studied in molecular detail. The long behavioral period of tim(L1) is reflected in a lengthened molecular oscillation of per and tim RNA and protein levels. The lengthened period is partly caused by delayed nuclear translocation of TIM(L1) protein, shown directly by immunocytochemistry and indirectly by an analysis of the phase response curve of tim(L1) flies.