Transcriptional organization of the convergent overlapping dnaQ-rnh genes of Escherichia coli.

The transcriptional organization was determined for the DNA polymerase III epsilon subunit (dnaQ) and the ribonuclease H (rnh) genes, which are closely spaced and organized in a face-to-face system (Maki, H., Horiuchi, T., and Sekiguchi, M. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 7137-7141). Nuclease S1 mapping revealed that transcription starts from a single promoter for rnh and two promoters for dnaQ and proceeds in opposite directions. The 5' terminus of the rnh RNA overlaps about 100 and 20 nucleotide sequences with the 5' terminus of the dnaQ-1 and dnaQ-2 RNA, respectively. The levels of in vivo transcription for the three RNA species increased altogether by more than 10-fold in cells carrying a multicopy plasmid with intact dnaQ-rnh genes, keeping the relative level for the convergent transcription units nearly constant.