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.