Tousled-like kinases (TLKs) constitute a family of serine/threonine kinases conserved in plants and animals that act in a cell cycle-dependent manner. In mammals, their activity peaks during S phase, when they phosphorylate the antisilencing function protein 1 (ASF1), a histone chaperone involved in replication-dependent chromatin assembly. Here, we show that Drosophila ASF1 is also a phosphorylation target of TLK, and that the two components cooperate to control chromatin replication in vivo. By altering TLK activity through loss-of-function mutations, we show that nuclear divisions are arrested at interphase, followed by apoptosis. Overexpression of TLK alters the chromatin structure, suggesting that TLK mediates the activity of chromatin proteins. These results suggest that TLK coordinates cell cycle progression through the regulation of chromatin dynamics.
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