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Genetic mapping and sequencing in mice confirmed the identification of the mammalian gene, clock, involved in the circadian system. A comparison of the nucleotide sequence of the wildtype gene with the previously described Clock mutant revealed a single nucleotide change, an A-T transversion in intron 19. This SNP results in the deletion of exon 19 in the clock gene and a 51 amino acid deletion in the CLOCK protein.
The authors also found widespread expression of clock within several murine tissues and conserved clock gene sequences in other organisms, demonstrating the important function of this gene within the circadian system.