Abstract

TheClockgene is an essential regulator of circadian rhythms. It encodes a member of the basic helix-loop-helix/PER-ARNT-SIM family of transcription factors known to play a central role in the control of diverse cellular events. Previously we described the functional identification and molecular isolation of theClockgene in the mouse, its interaction with the BMAL1 protein, and the role of this complex as a transcriptional activator in the circadian pacemaker. Here, we report the cloning, exon organization, chromosomal location, and mRNA expression of the humanCLOCKgene. The coding sequence of humanCLOCKextends for 2538 bp and is 89% identical to its mouse ortholog; its deduced amino acid sequence is 846 residues long and is 96% identical to mouse CLOCK. Radiation hybrid mapping localized humanCLOCKto the long arm of human chromosome 4 (4q12). Direct sequencing of a genomicCLOCKclone indicated that the coding sequence of humanCLOCKextends over 20 exons and that its intron/exon organization is identical to that of the mouse ortholog. Northern blot analysis indicated widespread expression of two major transcripts of 8 and 10 kb, andin situhybridization of human brain tissue revealed elevated expression ofCLOCKmRNA in the suprachiasmatic nuclei, the locus of circadian control in mammals, and in the cerebellum. Comparison of cDNA clones revealed two single nucleotide polymorphisms in noncoding sequence flanking theCLOCKopen reading frame. The central role ofClockin the organization of circadian rhythms suggests that it will be a useful candidate gene for genetic analyses of disorders associated with dysfunction of the circadian system.