Recombinant retroviral intasomes assembled from purified integrase (IN) and oligonucleotides mimicking viral DNA ends (vDNA) faithfully recapitulate concerted integration in vitro. Structural studies of retroviral intasomes have revealed an array of IN oligomer forms, which appear to share a conserved intasome core coordinating the vDNA ends for strand transfer into target DNA. Here we have explored the biochemical and dynamic properties of the mouse mammary tumor virus (MMTV) octameric intasome. We show that MMTV intasomes continue to accumulate concerted integration products for ~80 min in vitro, whereas prototype foamy virus (PFV) intasomes plateau within ~2 min. MMTV integration activity peaks within the range of physiological ionic strength and is more active in the presence of manganese compared to magnesium. Single-molecule images demonstrate that the target DNA search by MMTV intasomes appears rate-limiting, similar to PFV intasomes. The time between strand transfer of the two MMTV vDNA ends into the target DNA is ~ 3 fold slower than PFV intasomes. This is the first report of the dynamics of an orthoretrovirus intasome interacting with target DNA with single molecule resolution.
Baltierra-Jasso et al. (Fri,) studied this question.