Abstract
We report the identification, characterization, and cloning of another novel
Drosophila clock gene,
cycle (
cyc). Homozygous
cyc flies are completely arrhythmic. Heterozygous
cyc/+ flies are rhythmic but have altered periods, indicating that the
cyc locus has a dosage effect on period. The molecular circadian phenotype of homozygous
cyc flies is like homozygous
Clk flies presented in the accompanying paper: mutant flies have little or no transcription of the
per and
tim genes. Cloning of the gene indicates that it also encodes a bHLH-PAS transcription factor and is a
Drosophila homolog of the human protein BMAL1.
cyc is a nonsense mutation, consistent with its strong loss-of-function phenotype. We propose that the CYC:CLK heterodimer binds to
per and
tim E boxes and makes a major contribution to the circadian transcription of
Drosophila clock genes.