Simplification of topology during Xer-mediated recombination
Seminar Room 1, Newton Institute
The chromosome of the bacterium Escherichia coli is a single circular DNA molecule of about 4.6 Mbp. Various recombinational repair processes that act upon the DNA during or following its replication can lead to a genetic crossover occurring, which in turn leads to a chromosome dimer being formed. This requires resolution back to two un-catenated single chromosomes before the cell can divide. The dimer resolution reaction is catalysed by the two recombinase proteins, XerC and XerD. Catalysis by XerD is in turn controlled by protein-protein interaction with the gamma subdomain of the FtsK DNA translocase. Recent in vitro data has shown that the interaction between XerD and FtsK-gamma is sufficient to stimulate recombination, but that in the absence of the DNA translocation motor of FtsK, then complex toplogical products result. If the motor is added back to these reactions, then simple, unlinked circular products are seen. DNA translocation is required for efficient chromosome dimer resolution in vivo too, mirroring the other experimental results. The focus of current research is into how XerD catalytic activity is stimulated, and how DNA translocation by FtsK leads to products with a simple toplogy.