MOLECULAR ANALYSIS OF THE LACTOCOCCUS-LACTIS SUBSPECIES LACTIS CNRZ270 BIDIRECTIONAL THETA REPLICATING LACTOSE PLASMID PUCL22

pUCL22 is the lactose protease plasmid of Lactococcus lactis ssp. lact is CNRZ270. The nucleotide sequence of its replication region Rep22 co ntains a non-transcribed region, the replication origin, followed by a gene encoding a putative 388-amino-acid protein named Rep22A. The pro moter regions of the rep22A and pC194 cat genes share strong similarit ies and the pUCL22 replicon exerted trans or cis negative control on t he pC194 cat gene expression in L. lactis. We suggest that Rep22A bind s to its own promoter as well as to the pC194 cat promoter and thus is autoregulated. We show that pUCL22 replicates mainly by a bidirection al theta mechanism in L. lactis, and is representative of a widely dis tributed replicon family, members of which could be co-resident. We pr opose that compatibility between these closely related replicons resul ts from minor replication protein modifications coupled with base chan ges in their respective binding sites, supporting the co-existence of numerous related replicons in lactococcal strains.