Abstract
The integrase (IN) protein of the human immunodeficiency virus (HIV) mediates two distinct reactions: (i) specific removal of two nucleotides from the 3' ends of the viral DNA and (ii) integration of the viral DNA into target DNA. Although IN discriminates between specific (viral) DNA and nonspecific DNA in physical in vitro assays, a sequence-specific DNA-binding domain could not be identified in the protein. A nonspecific DNA-binding domain, however, was found at the C terminus of the protein. We examined the DNA-binding characteristics of HIV-1 IN, and found that a stable complex of IN and viral DNA is formed in the presence of Mn2+. The IN-viral DNA complex is resistant to challenge by an excess of competitor DNA. Stable binding of IN to the viral DNA requires that the protein contains an intact N-terminal domain and active site (in the central region of the protein), in addition to the C-terminal DNA-binding domain.