REPLICATION TERMINUS FOR DNA-POLYMERASE-I DURING INITIATION OF PAM-BETA-1 REPLICATION - ROLE OF THE PLASMID-ENCODED RESOLUTION SYSTEM

Replication of plasmid pAM beta 1 is initiated by DNA polymerase I (po i I) and completed by DNA polymerase III holoenzyme contained in the r eplisome machinery. In this study we report that initiation of DNA rep lication generates D-loop structures containing the nascent leading st rand paired to its template, and that D-loop extension is arrested app roximate to 230 bp from the initiation site of DNA synthesis in the pr esence of the plasmid-encoded resolvase. In vitro and in vivo data sug gest that this arrest is caused by a collision between poi I and the r esolvase bound to its target. As the arrested D-loop replication inter mediates carry a single-stranded primosome-assembly site, we hypothesi ze that the biological role of the replication arrest is to limit the region replicated by poi I and to promote the replacement of poi I by the replisome in order to initiate concerted synthesis of the leading and lagging strands.