FIG. 9.

Control of plasmid DNA replication. Examples of control by Rep DNA-binding sites (plasmid P1), by antisense RNAs (plasmids R1 and pT181), and by a dual system (plasmid pMV158) are depicted. Transcripts are shown as continuous lines, with arrowheads indicating the direction of synthesis. mRNAs are shown with thicker lines than antisense RNAs; countertranscribed RNAs (thin lines with small arrowheads) are indicated. Other symbols as follows: solid ellipses, origins; rectangles, promoters; a.r.b.s., atypical ribosome-binding site; parallel vertical lines, mRNA-ctRNA interactions; plus, positive interactions; minus, and inhibitory RNA-RNA or protein-DNA interactions.