Positional Cloning of the Mouse Circadian Clock Gene

King DP, Zhao Y, Sangoram AM, Wilsbacher LD, Tanaka M, Antoch MP, Steeves TD, Vitaterna MH, Kornhauser JM, Lowrey PL, Turek FW, Takahashi JS. Cell. 1997;89(4):641-53.

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.

Mutagenesis and Mapping of a Mouse Gene, Clock, Essential for Circadian Behaviour

Vitaterna MH, King DP, Chang AM, Kornhauser JM, Lowrey PL, McDonald JD, Dove WF, Pinto LH, Turek FW, Takahashi JS. Science. 1994;264(5159):719-25.

Using the mutagenic agent, N-ethyl-N-nitrosourea, a mutated lineage of mice was generated with an inheritable phenotype of altered circadian rhythmicity. Wildtype mice maintained normal circadian rhythms in constant darkness with a period of 23.3 – 24 hours, whereas mice heterozygous for the mutation showed a lengthening of the circadian period to approximately 24.4 hours in constant darkness. Homozygous mutant offspring showed the greatest change in circadian phenotype, with an endogenous period of 26-29 hours in the initial weeks under constant dark conditions, after which the animals became arrhythmic.

This genetic mutation was mapped to the midportion of mouse chromosome 5, identifying the novel circadian gene, clock, a key factor regulating the circadian clock system.