on 10-27-201410:27 AM - edited on 10-15-202110:27 AM by Closed Account
Klimovskaia IM, Young C, Strømme CB, Menard P, Jasencakova Z, Mejlvang J, Ask K, Ploug M, Nielsen ML, Jensen ON, Groth A. Nat Commun. 2014 Mar 6;5:3394. doi: 10.1038/ncomms4394. 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.