DNA-BINDING PROPERTIES OF THE ZINC-BOUND AND ZINC-FREE HIV NUCLEOCAPSID PROTEIN - SUPERCOILED DNA UNWINDING AND DNA-PROTEIN CLEAVABLE COMPLEX-FORMATION

The HIV nucleocapsid (NC) protein contains, as those of other retrovir uses, two Cys-His arrays which function as zinc finger binding domains . The nucleic acid binding properties of retroviral NC have been previ ously demonstrated. In this study, we characterized the DNA binding ab ility of the zinc-bound and zinc-free forms of HIV NC. We found that i n addition to binding single-stranded DNA, both forms bind and unwind supercoiled plasmid DNA. The binding ability of the zinc-bound form wa s higher than the zinc-free form. In addition we showed the formation of NC protein-DNA cleavable complex which is the result of a presumabl y covalent bond formed between the protein and the phosphate moiety of the DNA backbone. The NC unwinding activity and the protein-DNA cleav able complex formation resembles the first step of the relaxing mechan ism of DNA topoisomerase. Our results shed light on the possibility of a novel physiological function for the HIV NC protein in the viral li fe cycle.