MuLV IN mutants responsive to HDAC inhibitors enhance transcription from unintegrated retroviral DNA.

For Moloney murine leukemia virus (M-MuLV), sustained viral infections require expression from an integrated provirus. For many applications, non-integrating retroviral vectors have been utilized to avoid the unwanted effects of integration, however, the level of expression from unintegrated DNA is significantly less than that of integrated provirus. We find that unintegrated DNA expression can be increased in the presence of HDAC inhibitors, such as TSA, when applied in combination with integrase (IN) mutations. These mutants include an active site mutation as well as catalytically active INs bearing mutations of K376 in the MuLV C-terminal domain of IN. MuLV IN K376 is homologous to K266 in HIV-1 IN, a known substrate for acetylation. The MuLV IN protein is acetylated by p300 in vitro, however, the effect of HDAC inhibitors on gene expression from unintegrated DNA is not dependent on the acetylation state of MuLV IN K376.