During DNA replication, nucleosomes are rapidly assembled on newly synthesized DNA to restore chromatin organization. Asf1, a key histone H3-H4 chaperone required for this process, is phosphorylated by Tousled-like kinases (TLKs). Here, we identify TLK phosphorylation sites by mass spectrometry and dissect how phosphorylation has an impact on human Asf1 function. The divergent C-terminal tail of Asf1a is phosphorylated at several sites, and this is required for timely progression through S phase. Consistent with this, biochemical analysis of wild-type and phospho-mimetic Asf1a shows that phosphorylation enhances binding to histones and the downstream chaperones CAF-1 and HIRA. Moreover, we find that TLK phosphorylation of Asf1a is induced in cells experiencing deficiency of new histones and that TLK interaction with Asf1a involves its histone-binding pocket. We thus propose that TLK signalling promotes histone supply in S phase by targeting histone-free Asf1 and stimulating its ability to shuttle histones to sites of chromatin assembly.
Nature Communications, 2014, Vol 5
Journal Article; Research Support, Non-U.S. Gov't; Amino Acid Sequence; Binding Sites; Blotting, Western; Cell Cycle Proteins; Cell Line, Tumor; Chromatin; DNA Replication; HeLa Cells; Histones; Humans; Mass Spectrometry; Microscopy, Confocal; Molecular Chaperones; Mutation; Phosphorylation; Protein Binding; Protein-Serine-Threonine Kinases; RNA Interference; S Phase