Plays an important role in the control of DNA replication, maintenance of replication fork stability, maintenance of genome stability throughout normal DNA replication, DNA repair and in the regulation of the circadian clock (PubMed:9856465, PubMed:23418588, PubMed:10428031, PubMed:12875843). Required to stabilize replication forks during DNA replication by forming a complex with TIPIN: this complex regulates DNA replication processes under both normal and stress conditions, stabilizes replication forks and influences both CHEK1 phosphorylation and the intra-S phase checkpoint in response to genotoxic stress (PubMed:12875843). TIMELESS promotes TIPIN nuclear localization (PubMed:12875843). Involved in cell survival after DNA damage or replication stress by promoting DNA repair (PubMed:12875843). In response to double-strand breaks (DSBs), accumulates at DNA damage sites and promotes homologous recombination repair via its interaction with PARP1 (By similarity). May be specifically required for the ATR-CHEK1 pathway in the replication checkpoint induced by hydroxyurea or ultraviolet light (PubMed:23418588). Involved in the determination of period length and in the DNA damage-dependent phase advancing of the circadian clock (PubMed:23418588, PubMed:10428031). Negatively regulates CLOCK|NPAS2-ARTNL/BMAL1|ARTNL2/BMAL2-induced transactivation of PER1 possibly via translocation of PER1 into the nucleus (PubMed:9856465). May also play an important role in epithelial cell morphogenesis and formation of branching tubules (PubMed:10963667). Homodimer or homomultimer (PubMed:12875843, PubMed:23418588). Component of the circadian core oscillator, which includes the CRY proteins, CLOCK or NPAS2, ARTNL/BMAL1 or ARTNL2/BMAL2, CSKN1D and/or CSNK1E, TIMELESS, and the PER proteins (PubMed:9856465). Interacts directly with PER2; the interaction with PER2 is via its second PAS domain (PubMed:14564007). Interacts directly with PER1 and PER3 (PubMed:9856465, PubMed:10231394, PubMed:14564007). Interacts with CRY1 (PubMed:10428031, PubMed:23418588, PubMed:24489120). Interacts with CRY2 (PubMed:10428031). Interacts with CHEK1, ATR and ATRIP (By similarity). Interacts with CLSPN (By similarity). Interacts with TIPIN (PubMed:12875843). Interacts with DDX11; this interaction increases recruitment of both proteins onto chromatin in response to replication stress induction by hydroxyurea (By similarity). Interacts with PARP1; interaction is direct and independent of poly-ADP-ribose (By similarity). In response to double-strand breaks (DSBs), accumulates at DNA damage sites via its interaction with PARP1. Predominantly and robustly expressed in proliferative organs (spleen, thymus, intestine and testis) compared to those more differentiated such as kidney and liver (at protein level). Expressed in all tissues examined including brain, heart, lung, liver, skeletal muscle, kidney, placenta, pancreas, spleen, thymus and testis. Strongly expressed in the suprachiasmatic nucleus (SCN) and pars tuberalis, moderately in the cingulate cortex, pyrimidal cell layer of the piriform cortex, periventricular part of the caudate putamen, and granular layer of the cerebellum, and weakly in the cerebral cortex, gyrus dentatus, hippocampus and thalamic nuclei. In embryonic kidney, expression is highest in regions of active ureteric bud cell branching. Expression is highest in whole embryos at 11 dpc and gradually decreases as embryonic development progresses. At 7.5 dpc, expressed in germ cell layers. At 14.5 dpc, expressed at highest levels in thymus, liver, gastrointestinal tract, lung and the rapidly proliferating ventricular zone of the brain. In retina, expression exhibits a circadian rhythm in the presence of light/dark cycles. In the suprachiasmatic nucleus (SCN), isoform 1 exhibited 24 hours oscillation, isoform 4 is constitutively expressed. Shows a circadian expression pattern in the intestine with peaks at ZT4 and ZT8. Belongs to the timeless family. Contaminating sequence. Potential poly-A sequence. Contaminating sequence. Potential poly-A sequence.