HIV-I replication requires an intact integrase reading frame.

Human immunodeficiency virus type I (HIV-I), is a human retrovirus that is the causative agent of acquired immune deficiency syndrome (AIDS). Retroviruses replicate through a DNA intermediate. After initial synthesis of unintegrated DNA the insertion of that DNA into the host cell genome is thought to be a required step in the retrovirallife cycle [1]. A hallmark of HIV-I infection, however, is the persistent appearance oflarge amounts of unintegrated DNA. Integrated DNA is often difficult to detect, and is readily detectable only after extensive passage of infected cell lines. Consequently, it is not clear that integration is an obligatory part of the HIV-I life cycle. To test the need for integration in HIV-I replication and expression, we have introduced point mutations including a stop codon into the COOH terminal part of the POL gene containing the integrase coding region and substituted this region for the analogous region of the biologically active molecular clone of HIV-I, pHXB2D [2]. Transfection of cos-I cells with the INT mutant resulted in transient expression of biologically active virus. However, infection of H9 cells with the mutant virus yielded neither detectable persistent media reverse transcriptase activity nor viral GAG antigen. These results suggest that integration of proviral DNA is a necessary part of the productive infection of T -cells. After infection, retroviral DNA synthesis results in three types of unintegrated DNA: the linear double-stranded