Transcripts within the replication origin, oriC, of Escherichia coli.

Transcription start and termination sites were mapped in the E. coli replication origin, oriC. Outward transcription from within oriC (promoters Pori-r and Pori-l) was found to start in vivo at position 178 for Pori-l and at positions 294 and 304 for Pori-r, respectively. These transcripts were terminated after 100-150 bases, at terminators designated Tori-l and Tori-r. Transcription from the 16 kd promoter, which lies clockwise adjacent to oriC and promotes transcription toward oriC, started at position 757 and gave transcripts with 3' ends at several positions within and to the left of the minimal replication origin. However, the majority of transcripts traversed the whole oriC region, and were not terminated within the DNA segment tested. Transcription of the chromosomal 16 kd gene was negatively regulated by DnaA protein and positively affected by dam methylation. The possible function of these transcripts is discussed.