Figure 1.

Diagram of the potential sites for replicon cointegration in the S. meliloti genome. (I) Schematic representation of the points of recombination between a repeated family containing 1 element (a) in replicon A and two elements (b,c) located in inverted orientation in replicon B. Each element is represented by a large arrow indicating the orientation; the small arrows indicate the primers bordering each element. Primers are indicated by numbers: 1, primer at the 5′-end of element a; 2, primer at the 3′-end of element a; 3, primer at the 5′-end of element b; 4, primer at the 3′-end of element b; 5, primer at the 3′-end of element c; 6, primer at the 5′-end of element c. The lines linking the two replicons indicate potential points for recombination leading to cointegration. To detect cointegration by the PCR method (see text), the following primers are used: for cointegration by a and b elements, primers 1 and 4 or 2 and 3; for cointegration by a and c elements, primers 1 and 5 or 2 and 6. (II) The three replicons of the genome of S. meliloti 1021 are represented by circles: A, pSymA, B, pSymB, C, chromosome. The area is proportional to the length of each replicon. The origin of replication is represented by O; the direction of the annotation is clockwise according to that reported (Galibert et al. 2001; http://sequence.toulouse.inra.fr/meliloti.html). Repeated sequences with more than 95% sequence similarity in a track of at least 1 kb and present in more than one replicon were localized. Each pair of repeated sequences that might recombine generating replicon cointegrations is represented by a line linking two replicons at the corresponding sites of the repeats.