Multiple effects of mutations in human immunodeficiency virus type 1 integrase on viral replication

The integration of a DNA copy of the human immunodeficiency virus type 1 (HIV-1) genome into a chromosome of an infected cell is a pivotal step in virus replication. Integration requires the activity of the virus-encoded integrase, which enters the cell as a component of the virion. Results of numerous mutagenesis studies have identified amino acid residues and protein domains of HIV-1 integrase critical for in vitro activity, but only a few of these mutants have been studied for their effects on HIV replication. We have introduced site-directed changes into an infectious DNA clone of HIV-1 and show that integrase mutations can affect virus replication at a variety of steps. We identified mutations that altered virion morphology, levels of particle-associated integrase and reverse transcriptase, and viral DNA synthesis. One replication-defective mutant virus which had normal morphology and protein composition displayed increased levels of circular viral DNA following infection of a T-cell line. This virus also had a significant titer in a CD4-positive indicator cell assay, which requires the viral Tat protein. Although unintegrated viral DNA can serve as a template for Tat expression in infected indicator cells, this level of expression is insufficient to support a spreading viral infection in CD4-positive lymphocytes.