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Humans
The human timeless protein (hTIM) has been shown to be required for the production of electrical oscillations output by the suprachiasmatic nucleus (SCN), the major clock governing all tissue-specific circadian rhythms of the body. This protein also interacts with the products of major clock genes CLOCK, BMAL, PER1, PER2 and PER3.

Sancar and colleagues investigated whether hTIM played a similar role to orthologs in C. elegans and other types of yeast, which are known to play important roles in the cell cycle. Their experiments suggested that hTIM plays an integral role in the G2/M and intra-S cell cycle checkpoints. With respect to the G2/M checkpoint, hTIM binds to the ATRIP subunit on ATR – a protein kinase sensitive to DNA damage. This binding between hTIM and ATR then leads to the phosphorylation of Chk1, resulting in cell cycle arrest or apoptosis. This process serves as an important control to stop the proliferation of cells with DNA damage prior to mitotic division. The role of hTIM in the intra-S checkpoint is less clear at the molecular level. However, down-regulation of hTIM leads to an increase in the rate of generation of replication forks – even in the presence of DNA damage and other regulatory responses. Timeless gene has also been found to influence the development of disease in humans. Downregulation of Timeless gene in human carcinoma cells leads to shortened telomeres, indicating its role in telomere length maintenance. Telomere-associated DNA damage also increases in timeless depleted cells, along with the delay of telomere replication. This association between Timeless and telomeres is indicative of the genes possible association with cancer. That makes sense