FIGURE 2.

Rolling-circle replication (RCR) in conjugal transfer. The individual stages of DNA synthesis during plasmid conjugal transfer (1–5). The RCR initiation protein (relaxase) containing two conserved tyrosine residues, Y1 and Y2, initiates (+) strand replication at the nick site (marked by a yellow rectangle). Both Y1 and Y2 may be involved in DNA processing during the transfer (plasmid R388) (3a, 4a), or only one of them – Y1 (plasmid F) (3b, 4b) (see text for details). Dashed blue lines indicate the nascent DNA strand and blue arrows show the direction of synthesis. Black dotted arrows indicate nucleophilic attack of the catalytic tyrosine residue on the phosphodiester bond in the DNA or of the free 3′-OH DNA end on the phosphotyrosine bond between the enzyme and the DNA (adopted from Chandler et al., 2013).