Tousled-like kinase 1 (TLK1) is a serine/threonine kinase involved in chromatin assembly and the DNA damage response. The tousled (Tsl) kinase was first identified in Arabidopsis thaliana and speculated to be involved in cell division during patterning of plant organs. There are two tousled-like kinases in humans, TLK1 and TLK2, that can dimerize or heterodimerize for function and can be phosphorylated and inactivated by Chk1 in response to DNA damage. The histone chaperone, Asf1 (anti-silencing function 1), has been reported as a substrate for both TLK1 and TLK2. TLK1 has also been shown to be important for cell cycle progression and proper chromosome segregation.