Replication termination for staphylococcal plasmids: plasmids pT181 and pC221 cross-react in the termination process

We present data which indicate that (i) the origin of replication of plasmids pT181 and pC221 can also function as termination signals; (ii) termination of replication occurs when a round of replication initiated either by RepC at the pT181 origin or by RepD at the pC221 origin reaches either of these origins, proving that the two plasmids cross-react for termination of replication; and (iii) the replication initiated at the origin of another staphylococcal plasmid, pE194, does not terminate at the origin of pT181 or pC221, indicating the existence of a specific relationship between the initiation and termination of a replication event. The process of replication can be divided into three steps: initiation, elongation, and termination. The initiation process has been studied in great detail for many different bacterial replicons, since it represents the step that involves specific interactions which confer the property of autonomous repli-cation; i.e., once it is initiated a round of replication pro-ceeds until all the DNA covalently bound to the origin is duplicated. It is also the level at which most, if not all, regulatory mechanisms affecting replication act. Much less i