LOCALIZATION OF DNA-BINDING ACTIVITY OF HIV-1 INTEGRASE TO THE C-TERMINAL HALF OF THE PROTEIN

Human immunodeficiency virus type 1 (HIV-1) integrase (IN) is the viral protein required for integration of the HIV-1 genome into host cell DNA. A series of clones expressing portions of IN as lambda-cII fusion proteins has been constructed in an Escherichia coli expression system; a Southwestern procedure was used to examine binding of the expressed proteins to DNA oligonucleotides. Proteins expressed by clone pHIP106, encoding the entire IN protein but no other pol sequence, and pKNA101, which expresses an IN fusion protein containing 23 amino acids of HIV-1 reverse transcriptase at its amino terminus, exhibited similar levels of oligonucleotide binding. Little DNA sequence specificity was associated with binding activity and there was a preference for Mn2+ over Mg2+ and Ca2+. Interestingly, the protein expressed by an N-terminal clone containing nucleotides coding for IN amino acids 1-141 (including a conserved His-Cys box) was unable to bind oligonucleotide, whereas the protein expressed by a C-terminal clone containing nucleotides coding for amino acids 142-288 exhibited binding equivalent to that of full-length IN. The C-terminal protein was unreactive with a MAb to the lambda-cII leader peptide and with an antipeptide serum directed against amino acids 141-158. These results are consistent with the previously reported internal initiation of IN protein synthesis in E. coli at met 154, and indicate that the C-terminal clone does not express IN amino acids 142-153. These amino acids represent part of a conserved region termed D(35)E, containing amino acids 116-152, which has been implicated in IN DNA binding. Since the C-terminal sequences in IN bind DNA as well as the entire IN protein, our findings suggest that amino acids 154-288 are sufficient for DNA binding and that the conserved region, D(35)E, may not be required.