Membrane-protein phosphorylation in the Bacillus subtilis cell cycle

Sphingosine, an inhibitor of Ca²⁺-dependent protein kinases in eukaryotic cells, inhibited initiation of DNA replication in Bacillus subtilis at a concentration of 10 μM, without inhibiting elongation. The tumor promoter 12-tetradecanoyl 13-phorbol acetate, (TPA), an activator of protein kinase C in eukaryotic cells, partially counteracted the inhibition of initiation by sphingosine. Phosphorylation of polypeptides was observed in vivo at initiation of DNA replication in B. subtilis. Sphingosine, TPA, and vancomycin affected this protein phosphorylation.