STAUROSPORINE SUPPRESSES REPLICON INITIATION IN MAMMALIAN-CELLS

Replication in cellular replicons of mouse Ehrlich ascites, human CCRF -CEM and hamster BHK-21 cells was analyzed, after exposition of the ce lls to staurosporine, by measuring the overall DNA synthesis rate, by alkaline sedimentation analysis of length distributions of growing dau ghter strand DNA and by DNA fibre autoradiography. The results consist ently indicated that micromolar concentrations of staurosporine caused , in all three cell lines, a fast suppression of replicon initiation w hich was reversible if the drug treatment did not exceed about 2 h. Th e inhibition of initiation was accompanied by a slight reduction of ra tes of propagation of replication forks. The data are interpreted in t erms of the existence of a so far unknown factor which seems to be inv olved relatively directly in the initiation process of cellular replic ons and has to be activated, like the large T antigen of SV 40 for the replication initiation in the viral genome, by a specific phosphoryla tion event. Unlike several other protein phosphorylations of cellular regulation, the kinase concerned here seems to be inhibited only by re latively high staurosporine concentrations.