Two basic regions of NCp7 are sufficient for conformational conversion of HIV-1 dimerization initiation site from kissing-loop dimer to extended-duplex dimer

Nucleocapsid (NC) protein possesses nucleotide-annealing activities, which are used in various processes in retroviral life cycle. As conserved charac ters, the NC proteins have one or two zinc fingers of CX2CX4HX4C motif surr ounded by basic amino acid sequences. Requirement of the zinc fingers for t he annealing activities of NC protein remains controversial. In this study, we focused the requirement in the process of maturation of dimeric viral R NA. Discrimination between immature and mature dimers of synthetic RNA corr esponding to the dimerization initiation site of human immunodeficiency vir us type 1 (HIV-1) genomic RNA was performed based on their Mg2+-dependent s tability in gel electrophoreses and on their distinct signal pattern from N MR analysis of imino protons. Chaperoning activity of the HIV-1 NC protein, NCp7, and its fragments for maturation of dimeric RNA was investigated usi ng these experimental systems. We found that the two basic regions flanking the N-terminal zinc finger of NCp7, which are connected by two glycine res idues instead of the zinc finger, were sufficient, although about 10 times the amounts of peptide were needed in comparison with intact NCp7. Further, it was found that the amount of basic residues rather than the amino acid sequence itself is important for the activity. The zinc fingers may involve the binding affinity and/or such a possible specific binding of NCp7 to di merization initiation site dimer that leads to the maturation reaction.