TI - MAP kinases mediate UVB -induced phosphorylation of histone H3 at serine 28 . AB - Histone H3 phosphorylation is related closely to chromatin remodeling and chromosome condensation . H3 phosphorylation at serine 28 is coupled with mitotic chromosome condensation in diverse mammalian cell lines . However , the pathway that mediates phosphorylation of H3 at serine 28 is unknown . In the present study , ERK1 , ERK2 , or p38 kinase strongly phosphorylated H3 at serine 28 in vitro . JNK1 or JNK2 was able also to phosphorylate H3 at serine 28 in vitro but to a lesser degree . UVB irradiation markedly induced phosphorylation of H3 at serine 28 in JB6 Cl 41 cells . PD 98059 , a MEK1 inhibitor , and SB 202190 , a p38 kinase inhibitor , efficiently repressed UVB-induced H3 phosphorylation at serine 28 . Expression of dominant negative mutant ( DNM ) ERK2 in JB6 Cl 41 cells totally blocked UVB -induced phosphorylation of H3 at serine 28 . Additionally , DNM p38 kinase or DNM JNK1 partially blocked UVB-induced H3 phosphorylation at serine 28 . Furthermore , UVB-induced H3 phosphorylation at serine 28 was inhibited in Jnk1(-/-) cells but not in Jnk2(-/-) cells . These results suggest that UVB-induced H3 phosphorylation at serine 28 may be mediated by mitogen -activated protein kinases .