DISPLACEMENT OF VIRAL-DNA TERMINI FROM STABLE HIV-1 INTEGRASE NUCLEOPROTEIN COMPLEXES INDUCED BY SECONDARY DNA-BINDING INTERACTIONS

The human immunodeficiency virus type-I (HIV-I) integrase is known to form a highly stable interaction with the termini of the linear, pre-i ntegrated retroviral genome, where it catalyzes the 3'-OH processing a nd strand transfer processes required for their coordinated integratio n into host DNA. Here, we determine that the association of HIV-1 inte grase with the viral DNA termini leads to the formation of two classes of nucleoprotein complexes with distinct properties in vitro, Both bo und stales are intrinsically stable and highly resistant to exonucleas e digestion, but nonetheless they exhibit different stabilities in the presence of single-stranded polynucleotides. While a population of pr eassembled complexes tolerates elevated polynucleotide concentrations, the remainder forms an unstable ternary (integrase-substrate-polynucl eotide) intermediate, leading to the rapid expulsion of the otherwise tightly bound substrate, The distribution of complexes between the two states is influenced by the preincubation time and temperature, incre ases in either of which favor the formation of the challenge-resistant species. Challenge-resistant complexes are formed more efficiently wi th Mn2+ than with Mg2+ and are sensitive to the length rather than the sequence of the DNA substrate. Due to the delayed appearance of the c hallenge-resistant form after the initial stable binding of the DNA su bstrate, our results may be indicative of a structural change in the p reassembled complex which thereby modulates its response to exogenous DNA targets.