Fig 7.

Models of strand exchange caused by ZfL2-1 ORF1p. (A) Strand exchange model with independent base-pair dissociation and creation. If the dissociation and the creation are independent steps in strand exchange, dissociation is followed by creation. (B) Strand exchange model with interdependent base-pair dissociation and creation. If the dissociation is related to the creation, a branched structure is formed as a reaction intermediate. ZfL2-1 ORF1p facilitates formation of the intermediate. The branch point of the intermediate can move in both directions in a ZfL2-1 ORF1p-dependent or -independent manner. When the branch point moves back to the origin, the incoming single strand is released and the original double strand returns to the double-stranded form (left). On the other hand, when the branch point reaches the opposite end, the new double-stranded DNA forms and one strand of the original double strand is released (right).