Fig. 5

Strand exchange reactions promoted by RecA protein homologues. (a) A reaction with a linear dsDNA and a circular ssDNA that is the same as one strand of the linear DNA. DNA from bacteriophages M13 or φX174 can be used in this reaction. (a) RecA protein binds initially to the ssDNA (not shown). (b) The RecA-ssDNA invades the linear dsDNA by base pairing to one strand and displacing the other, forming a structure similar to a D-loop. (c) One linear strand is transferred completely to the circle (branch migration) to form linear ssDNA and nicked circular dsDNA products. (b) (d) RecA binds to an ssDNA gap in a circular dsDNA. (e) The RecA-ssDNA invades the linear dsDNA to form a D-loop. (f) The strand exchange extends into the dsDNA part of the circle to form a Holliday junction. (g) Branch migration gives circular and linear dsDNA products (After Cox 2007)