Functional relationship between the matrix proteins of feline and simian immunodeficiency viruses.

To investigate the functional relationship between the matrix (MA) proteins of feline and simian immunodeficiency viruses (FIV and SIV, respectively), we generated chimeric proviruses in which the MA-coding region of an SIV infectious molecular clone was partially or fully replaced by its FIV counterpart. Chimeric SIV proviruses containing the amino-terminal 36 residues or the central and carboxy-terminal regions of the FIV MA assembled into virions as efficiently as wild-type SIV. However, the resulting virions were noninfectious in single-cycle infectivity assays. Furthermore, a chimeric SIV provirus containing the entire FIV MA was found to be severely impaired in virion production due to inefficient membrane binding of the chimeric Gag polyprotein. Interestingly, the assembly defective phenotype of this chimeric Gag precursor could be reversed either by introducing the G31K/G33K double amino acid substitution in the FIV-derived MA domain or by coexpression with wild-type SIV Gag. Of note, a chimeric FIV provirus expressing the SIV MA not only assembled into particles as efficiently as wild-type FIV, but also replicated in feline T cells with wild-type kinetics. Our results thus provide novel information about the functional homology between the MA proteins of distantly related lentiviruses.