PSIP1 and HIV-1 infection: In order to clarify the INI1 - mediated inhibition and/or activation functions in the early stage of HIV-1 infection, we analyzed the structure-function relationships of a quaternary complex comprising the full length wild type HIV-1 IN, the full length wild-type LEDGF, the INI1 IN binding domain (174–289) (INI1-IBD) and viral U5 DNA.