BOSTON--June 1, 1998--Researchers at Harvard Medical School have identified a protein that partners with the mammalian CLOCK protein to regulate circadian rhythms. Together, the two proteins appear to induce transcription of circadian rhythm genes. Their findings are published in the June 5 Science.
The daily, or circadian, rhythms of fruit flies--and presumably of mammals as well--are driven by the switching on and off of genes in a handful of cells. Per is one gene known to be an integral part of the molecular clock of flies. Researchers have also identified mammalian genes similar to per.
When the per gene is switched on, it initiates the synthesis of messenger RNA. The mRNA is then dispatched outside the nucleus, where the Per protein is made. Per protein gradually accumulates in the cell for several hours and then, at some it moves swiftly into the nucleus, shutting off its own gene and ending the circadian cycle. Until now, it was unclear what turned on per.
Last year, researchers at Northwestern University identified the first mammalian circadian gene in mice, which they named Clock. Mice with mutated Clock genes have disrupted rest and activity patterns. But it was unclear how CLOCK, the protein encoded by this gene, controlled circadian rhythms.
Charles Weitz, HMS assistant professor of neurobiology, and his colleagues suspected that CLOCK might be involved in the transcriptional activation of the mammalian per gene and most likely needed a partner to do the job. They identified a protein that interacts with CLOCK, named BMAL1, and found that BMAL1 and CLOCK bind to transcription factor sites near one of the mammalian per genes, producing an increase in transcriptional activity. BMAL1 and the mutant version of CLOCK also bound to the same sites, but no transcriptional activity resulted.