In vivo 5' terminus and length of the mRNA for the proton-translocating ATPase (unc) operon of Escherichia coli

Abstract

The promoter for the proton-translocating ATPase (unc) operon of Escherichia coli was localized by using a plasmid promoter-screening vector system. S1 nuclease analysis, using the appropriate single-stranded DNA probe from this promoter region and in vivo mRNA, revealed that the 5' end of the in vivo unc mRNA initiates with a guanine residue 73 bases before the start of the proposed gene 1 or 474 bases before uncB. An in vivo unc mRNA species of approximately 7,000 nucleotides in length which initiates in the unc promoter region was shown to exist by RNA-DNA hybridization analysis. This unc mRNA species (based on DNA sequence analysis) is sufficient in length to contain all nine genes, gene 1 and uncBEFHAGDC. That gene 1 is cotranscribed with the unc genes was confirmed by using hybridization probes containing the promoter-proximal (gene 1) or -distal gene (uncC). No strong internal promoters within the unc operon were revealed with either the promoter-screening vector system or the RNA-DNA hybridization analysis. The 5' terminus and the length of the unc mRNA were found to be identical in cells grown either aerobically or anaerobically. The level of unc operon expression, as assayed with the unc promoter plasmid, did not significantly differ when cells bearing the plasmid were grown either aerobically or anaerobically.