Methylations of histone H3 lysine 9 and lysine 36 are functionally linked to DNA replication checkpoint control in fission yeast.

Recently, histone H4 lysine 20 and H3 lysine 79 methylations were functionally linked to DNA damage checkpoint. The crosstalk between histone methylation and the S-M checkpoint, however, has remained unclear. Here, we show that H3 lysine 9 (K9) and lysine 36 (K36) methylations catalyzed by two histone methyltransferases Clr4 and Set2 are involved in hydroxyurea (HU)-induced replication checkpoint. The clr4-set2 double mutants besides histone H3-K9 and K36 double mutants exhibited HU-sensitivity, a defective HU-induced S-M checkpoint, and a significant reduction of HU-induced phosphorylation of Cdc2. Intriguingly, the clr4-set2 double mutations impaired the HU-induced accumulation of a mitotic inhibitor Mik1. Double mutants in Alp13 and Swi6, which can specifically bind to H3-K36 and K9 methylations, exhibited phenotypes similar to those of the clr4-set2 mutants. Together, these findings suggest that methylations of histone H3-K9 and K36 by Clr4 and Set2 are functionally linked to DNA replication checkpoint via accumulation of Mik1.