Figure 11.

Proposed model for the process of template switching recombination in φ8. Normally, the 3′ end of the template plus strand (green) enters the polymerase and is arrested near the site of nascent minus-strand chain formation (A); as the minus strand (red) is synthesized the dsRNA leaves the polymerase through the exit pore (B). The 3′ end of the nascent chain can be displaced from the template (C). It can reanneal to the template, or it can anneal to an empty template (blue) (E). A plus-strand RNA that does not have a proper 3′ end can enter the polymerase, but the template is not arrested at the catalytic site (D). Instead, it passes through the polymerase and can scan backward and forward. When a nascent minus strand anneals to the empty template and the template moves back into the polymerase, the nascent chain can act as a primer to start minus-strand synthesis on the empty template (F). The result is a recombinant minus strand. Reproduced from Onodera et al. (2001).