DISTINCT FUNCTIONS AND REQUIREMENTS FOR THE CYS-HIS BOXES OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 NUCLEOCAPSID PROTEIN DURING RNA ENCAPSIDATION AND REPLICATION

The process of retroviral RNA encapsidation involves interaction betwe en trans-acting viral proteins and cis-acting RNA elements. The encaps idation signal on human immunodeficiency virus type I (HIV-1) RNA is a multipartite structure composed of functional stem-loop structures. T he nucleocapsid (NC) domain of the Gag polyprotein precursor contains two copies of a Cys-His box motif that have been demonstrated to be im portant in RNA encapsidation. To further characterize the role of the Cys-His boxes of the HIV-1 NC protein in RNA encapsidation, the relati ve efficiency of RNA encapsidation for virus particles that contained mutations within the Cys-His boxes was measured. Mutations that disrup ted the first Cys-His box of the NC protein resulted in virus particle s that encapsidated genomic RNA less efficiently and subgenomic RNA mo re efficiently than did wild-type virus. Mutations within the second C ys-His box did not significantly affect RNA encapsidation. In addition , a full complement of wild-type NC protein in virus particles is not required for efficient RNA encapsidation or virus replication. Finally , both Cys-His boxes of the NC protein play additional roles in virus replication.