THE METAL ION-INDUCED COOPERATIVE BINDING OF HIV-1 INTEGRASE TO DNA EXHIBITS A MARKED PREFERENCE FOR MN(II) RATHER THAN MG(II)

In this investigation, we examine the interaction between the human im munodeficiency virus type I integrase and oligonucleotides that reflec t the sequences of the extreme termini of the viral long terminal repe ats (LTRs). The results of gel filtration and a detailed binding densi ty analysis indicate that the integrase binds to the LTR as a high-ord er oligomer at a density equivalent to 10 +/- 0.8 integrase monomers p er 21-base pair LTR. The corresponding binding isotherm displays a Hil l coefficient of 2, suggesting that the binding mechanism involves the cooperative interaction between two oligomers. This interaction is qu ite stable, exhibiting a prolonged half-life (t1/2 approximate to 13 h ) in the presence of Mn2+ cations. Complexes were less stable when for med with Mg2+ (t(1/2) approximate to 1 h). The role of Mn2+ appears to be in the induction of the protein-protein interactions that stabiliz e the bound complexes, In terms of the 3'-end processing of the LTR, s imilar catalytic rates (k(cat) approximate to 0.06 min(-1)) were obtai ned for the stable complex in the presence of either cation. Hence, th e apparent preference observed for Mn2+ in standard in vitro integrati on assays can be attributed entirely to the augmentation in the DNA bi nding affinity of the integrase.