Prototype foamy virus integrase is promiscuous for target choice

Retroviruses have two essential activities: reverse transcription and integration. The viral protein integrase (IN) covalently joins the viral cDNA genome to the host DNA. Prototype foamy virus (PFV) IN has become a model of retroviral intasome structure. However, this retroviral IN has not been well-characterized biochemically. Here we compare PFV IN to previously reported HIV-1 IN activities and discover significant differences. PFV IN is able to utilize the divalent cation calcium during strand transfer while HIV-1 IN is not. HIV-1 IN was shown to completely commit to a target DNA within 1 min, while PFV IN is not fully committed after 60 min. These results suggest that PFV IN is more promiscuous compared to HIV-1 IN in terms of divalent cation and target commitment.