Promoters in the E-coli replication origin

Chromosomal replication in Escherichia coli initiates at a particular sequence in the parental DNA called the origin of replication (oriC) and proceeds bidirectionally(1). Initiation requires the interaction of various factors at a given time within the cell cycle, including RNA polymerase(2,3). Recently, mini-chromosomes have been constructed(4,6) and partially sequenced(7,8) whose replication proved also to be dependent on a rifampicin-sensitive host function in addition to the products of several initiation genes(6,9). Using one of these mini-chromosomes, pCM959(6,8), we have searched for promoters in and close to oriC to elucidate the role of RNA polymerase in the initiation of replication. We have found, by In vitro transcription experiments and RNA sequencing, that the DNA segment required for the start of bidirectional replication in E. coli contains two promoters arranged back-to-back. The location and arrangement of these promoters suggest an involvement in the initiation of replication.