Multiple origins and replication proteins influence biological properties of beta-lactamase-producing plasmids from Neisseria gonorrhoeae

The beta -lactamase-producing Asia-type plasmid pJD4 of Neisseria gonorrhoe ae is a 7.4-kb, broad-host-range plasmid. It is part of a family of plasmid s which are structurally related yet vary in size, found in both N. gonorrh oeae and Haemophilus ducreyi. Branch-point analysis by electron microscopy indicates that pJD4 carries three clustered but distinguishable origins of replication, which we named ori1, ori2, and ori3. Although pJD4 belongs to incompatibility (Inc) group W, it also carries a silent IncFII determinant which is expressed when ori2 and ori3 are absent. The Africa-type plasmid p JD5, a naturally occurring deletion derivative of pJD4, carries only ori1, belongs to the IncFII group, and, in contrast to pJD4, requires DNA polymer ase I (Pol I) for replication. Plasmids constructed from pJD4 which lack or i1 but carry ori2 and ori3 do not require Pol I and are incompatible with I ncW plasmids, suggesting that the ori2 or ori3 region contains the IncW det erminant. We have cloned a replication initiation protein (RepB) that is ne cessary for ori2 and ori3 to function. This Rep protein is distinct from Re pA, which is necessary for ori1. Thus, pJD4 is unique because it is the sma llest plasmid characterized containing three origins of replication and two unique Rep proteins.