Figure 10.

Model of the in vitro IN positioning on viral ends. Interaction of monomers with short nonspecific nonviral DNA induces the formation of dimers inactive for processing, strand transfer and integration activities (type 2 dimers, way A). The interaction of monomers with the specific 21 nt viral DNA ends allow the formation dimers able to catalyze the processing and strand transfer reactions (type 1 dimers, way B). In the presence of longer DNA mimicking the viral genome and containing both short specific DNA regions and larger unspecific domains and in the absence of targeting, IN (standard in vitro conditions) will bind more frequently the nonspecific sequences (way A1). This will lead to the major formation of inactive type 2 dimers (A2). In solution and especially in associated IN preparations (concentrated one or enzyme purified in absence of detergent, in presence of Zn⁺⁺), preformed dimers (including types 1 and 2) are present. Type 1 dimers can bind the viral ends (B1) allowing the formation of the active tetrameric synaptic complex (SSC, B2).