THE CENTRAL GLOBULAR DOMAIN OF THE NUCLEOCAPSID PROTEIN OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 IS CRITICAL FOR VIRION STRUCTURE AND INFECTIVITY

The nucleocapsid protein NCp7 of human immunodeficiency virus type 1 ( HIV-1) is a 72-amino-acid peptide containing two CCHC-type zinc finger s linked by a short basic sequence, (29)RAPRKKG(35), which is conserve d in HIV-1 and simian immunodeficiency virus, The complete three-dimen sional structure of NCp7 has been determined by H-1-nuclear magnetic r esonance spectroscopy (N. Morellet, H. de Rocquigny, Y. Mely, N. Julli an, H. Demene, M. Ottmann, D. Gerard, J. L. Darlix, M. C. Fourni-Zalus ki, and B. P. Rogues, J. Mol. Biol. 235:287-301, 1994) and revealed a central globular domain where the two zinc fingers are brought in clos e proximity by the RAPRKKG linker, To examine the role of this globula r structure and more precisely of the RAPRKKG linker in virion structu re and infectivity, we generated HIV-1 DNA mutants in the RAPRKK seque nce of NCp7 and analyzed the mutant virions produced by transfected ce lls, Mutations that probably alter the structure of NCp7 structure led to the formation of very poorly infectious virus (A30P) or noninfecti ous virus (P31L and R32G). In addition, the P31L mutant did not contai n detectable amounts of reverse transcriptase and had an immature core morphology, as determined by electron microscopy. On the other hand, mutations changing the basic nature of NCp7 had poor effect, R29S had a wild-type phenotype, and the replacement of (32)RKK(34) by SSS (S3 m utant) resulted in a decrease by no more than 100-fold of the virus ti ter. These results clearly show that the RAPRKKG linker contains resid ues that are critical for virion structure and infectivity.