Histone phosphorylation in late interphase and mitosis

Abstract

Histone phosphorylation in late interphase has been investigated employing cells synchronized by the isoleucine-deprivation method, followed by resynchronization at the G 1 S boundary using hydroxyurea. Phosphorylation occurred in both f1 and f2a2 as cells synchronously entered S phase following removal of hydroxyurea. The relative rates of phosphorylation of both species of histone increased in G 2-rich and metaphase-rich cultures. A small amount of histone f3 phosphorylation was also observed in M-rich cultures which was not seen in G 1, S, or G 2-rich cultures. It is concluded that f1 phosphorylation is not dependent on continous DNA replication. These experiments suggest consideration of the concept that f1 phosphorylation is initiated as a preparation for impending cell division.