Figure 2. FtsK-dependent Xer recombination at dif as a tool to monitor sister chromatid contacts.

A. Scheme of the different site-specific recombination products that can be obtained when intramolecular recombination is impeded. B. Schematic representation of the 55 bp dif-recombination cassettes and the Xer recombination control set up. The orange arrow represents the lacZ gene disrupted by the two dif sites (red triangle). Expression of the xerC gene (green arrow) is under the positive control of the arabinose promoter, P_BAD, and the negative control of the E. coli lacZ promoter, P_Lac. C. dif1 and dif2 sequence divergence. The DNA binding arms of XerC and XerD are shown. Bases that differ in dif1 and dif2 are shown in red and blue, respectively. D. Reconstitution of a functional lacZ gene depends on XerC and FtsK. Results from at least three independent experiments. E. Recombination between dif sites harboured on different chromosomes does not perturb the SCC detection. Schematic representation of the genome of a strain harbouring lac2dif1 on chrII. No intrachromosomal recombination can occur between lac2dif1 and dif2 because of sequence divergence. The influence of chrI dif1 on chrII lac2dif1 recombination was tested by comparing results obtained in a strain in which dif1 was deleted. Results from at least three independent experiments. Legends as in Figure 1A. Red triangle: dif1; blue triangle: dif2.