The mouse mammary tumor virus intasome exhibits distinct dynamics on target DNA

Retroviral intasomes are complexes assembled from purified integrase (IN) and oligonucleotides mimicking viral DNA ends (vDNA). Recombinant intasomes faithfully recapitulate integration of vDNA into a target DNA. 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 the target DNA. Here we have explored the biochemical and dynamic properties of the mouse mammary tumor virus (MMTV) octameric intasome. We show that the MMTV intasome is remarkably stable compared to the prototype foamy virus (PFV) tetrameric intasome. 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. MMTV intasomes can form extremely stable, largely immobile filaments on a target DNA that are comprised of multiple intasomes. This unusual property suggests that MMTV intasomes may readily form higher order oligomers that might underpin their increased stability.