Cell cycle dependent phosphatase activity in Bacillus subtilis

In Bacillus subtilis there is evidence that the replication origin of the DNA molecule is attached to the cytoplasmic membrane, and that this attachment is essential for the initiation of replication. We have previously shown that attachment of DNA to the membrane is cyclic and that DNA becomes attached to the cytoplasmic membrane at the beginning of replication and is subsequently released. We have also shown that membrane protein phosphorylation is associated with the initiation of DNA replication in B. subtilis. We now report that cantharidin, an inhibitor of eukaryotic serine/threonine protein phosphatases type 1 and 2A, stimulated membrane binding of DNA and caused premature initiation of DNA replication in B. subtilis cells. The membrane of B. subtilis cells had cell cycle dependent phosphatase activity against a standard substrate in vitro. Cloning of the B. subtilis protein PrpE and production of antibodies allowed us to identify the protein in the cytoplasmic membrane. Its presence was cell cycle dependent, and appeared to contribute to the observed phosphatase activity.