Tn5 / IS50 structure and gene expression. (A) The structure of Tn5 is shown along with transcription units within IS50-Right. There are two distinct promoters defined by -35/-10 regions that control transposase (black) and inhibitor (blue) expression. T1 is the transposase transcript and T2 is the inhibitor transcript. The Shine-Dalgarno sequence of T1 is also shown. Expression of T1 but not T2 is regulated by DAM methylation at two GATC sequences (red) and potentially LexA binding (dotted line defines a putative LexA binding site). Mutations in the dam sites used in this work are shown. kanR, bleR and strR are kanamycin, bleomycin and streptomycin resistance genes, respectively. (B) Post-transcriptional regulation by Hfq. Hfq (blue hexamer) is shown catalyzing the pairing of an sRNA with an mRNA. The sRNA can be either cis or trans encoded relative to its target mRNA. In both cases the sRNA is shown pairing to the translation initiation region of the mRNA (asterisks) and would block translation.