Serine/threonine-protein kinase involved in the process of chromatin assembly and probably also DNA replication, transcription, repair, and chromosome segregation. Phosphorylates the chromatin assembly factors ASF1A AND ASF1B. Phosphorylation of ASF1A prevents its proteasome-mediated degradation, thereby enhancing chromatin assembly. Negative regulator of amino acid starvation-induced autophagy. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Cell cycle-regulated, with maximal activity in the S-phase. Rapidly and transiently inhibited by phosphorylation following the generation of DNA double-stranded breaks during S-phase, probably by CHEK1, possibly at Ser-750. This inhibition is cell cycle checkpoint- and ATM-dependent. Monomer and heterodimer with TLK1. Interacts with ASF1A and ASF1B. Association with 14-3-3 proteins such as YWHAZ regulates subcellular location. May also interact with FEZ1/LZTS1 and FEZ2. Colocalizes with the cytoplasmic intermediate filament system during the G1 phase of the cell cycle. Present in the perinuclear region at S phase and in the nucleus at late G2. Ubiquitous. Detected in placenta, fetal liver, kidney, pancreas, heart and skeletal muscle. Highly expressed in testis. Detected in spleen, thymus, colon, ovary, small intestine, prostate and peripheral blood leukocytes. Phosphorylated at Ser-750, probably by CHEK1. The disease is caused by variants affecting the gene represented in this entry. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.