Figure 1.

Branch migration assay. Two homologous duplexes (hatched) each having heterologous single-strand tails (black and white) are rapidly annealed to form a four-stranded structure with a Holliday junction. Two sets of substrates were used: S1 and S2 (300 bp homologous duplex) and R1 and R2 (273 bp homologous duplex). Spontaneous branch migration proceeds as a random walk until the junction reaches the distal end of the homologous region, leading to the irreversible dissociation of two duplex products. Asterisks indicate 5′-³²P-label.