The transcriptional pattern of the 22 min region of the Escherichia coli chromosome containing the linked sulA and ompA genes, which encode an SOS-inducible inhibitor of cell division and a constitutively expressed, major outer membrane protein, respectively, has been re-examined. During normal growth, the sulA gene was repressed whereas the ompA gene produced a stable 1250 nucleotide transcript. Counter-transcription of sulA occurred from a promoter situated in the sulA-ompA intergenic region and the product of this transcriptional circuit, named isf, is a 353 nucleotide untranslated RNA. Since the isf RNA is complementary to the 3'-end of the sulA transcript, it could modulate sulA function by serving as an anti-messenger. On induction of the SOS-response, massive transcription of sulA took place, resulting in the 'silencing' of the isf gene, production of an abundant approximately 615 nucleotide sulA mRNA and a novel hybrid transcript of approximately 2100 nucleotides encoding both the SulA and OmpA proteins. Production of the latter RNA species, caused by transcription reading through the sulA terminator, the intergenic region and the coding sequences, was accompanied by a decrease in the abundance of the ompA mRNA as a result of promoter occlusion. However, the amount of OmpA protein produced was only slightly reduced.