Biphasic increase in the in vivo phosphorylation of nuclear 110-kDa protein during early lymphocyte transformation

A major 110-kDa phosphoprotein in rat liver and hepatoma (P 110) was identified in nuclear 0.2 M HCl extracts from rat lymph node cells. Stimulation with concanavalin A altered both the amount of P110 and, more strikingly, its in vivo phosphorylation in a typical biphasic manner with an initial maximum after 10-14 h. RNA synthesis showed a similar biphasic increase. Inhibition of hnRNA synthesis (5,6 dichlorobenzimidazoleriboside), but not of DNA synthesis (hydroxyurea), depressed both the amount of P110 and its phosphorylation markedly.