The gag gene products of human immunodeficiency virus type 1: alignment within the gag open reading frame, identification of posttranslational modifications, and evidence for alternative gag precursors

Abstract

Seven human immunodeficiency virus gag polypeptides were identified in the purified virus and in infected CD4' lymphocytes by peptide mapping and limited amino acid sequencing of immune-purified proteins. Two gag polyproteins of 55,000 (p55) and 41,000 (p41) daltons were rapidly labeled and readily processed into the major internal gag proteins that were aligned within the gag open reading frame (ORF) as NH2-p16 (MA)-p24 (CA)-p9 (NC)-p7-COOH. The myristoylated p16 (matrix, MA) protein was processed from the myristoylated p55 gag precursor protein. The immunoreactivity of the p16 (MA) protein with region-specific gag antisera and the conservation of the N-terminal myristyl group of the p55 precursor protein in p16 (MA) confirmed its position as the N-terminal-most protein. The p9 (nucleocapsid, NC) protein was localized to residue 378 of the gag ORF, next to the C terminus of the p24/p25 (core antigen, CA) protein. The p9 protein had a repeating Cys residue-containing motif which is found in the nucleic acid-binding Cys residue-containing proteins of retroviruses. The p24 (CA) protein, which was localized to residue 133 of the gag ORF, was apparently derived by C-terminal processing of an intermediate polypeptide, p25. Both the mature p24 (CA) and p16 (MA) proteins were phosphorylated at Ser residue(s). We also identified two forms of gag p41 species, one resulting from the C-terminal processing of p55 and the other originating either from N-terminal processing of p55 or from de novo synthesis.

Proteolytic refolding of the HIV-1 capsid protein amino-terminus facilitates viral core assembly

“…It is increasingly clear that retroviral maturation proceeds via a highly ordered pathway (Mervis et al, 1988;Erickson-Viitanen et al, 1989;Göttlinger et al, 1989;Gowda et al, 1989;Tritch et al, 1991;Pettit et al, 1994;Kräusslich et al, 1995;Wiegers et al, 1997). This is perhaps not surprising, given that the viral core assembles de novo at very high Gag protein concentrations (Ͼ5 mM in the virion), where non-specific aggregation may pose a significant problem.…”

“…This is perhaps not surprising, given that the viral core assembles de novo at very high Gag protein concentrations (Ͼ5 mM in the virion), where non-specific aggregation may pose a significant problem. The rates of cleavage at the different HIV-1 Gag processing sites differ considerably (Mervis et al, 1988;Erickson-Viitanen et al, 1989;Gowda et al, 1989;Kräusslich et al, 1989;Pettit et al, 1994), and these differences may serve to release various Gag domains as they are needed for assembly of the mature virion. Consistent with this model, viral maturation arrests at morphologically distinct stages when the different Gag processing sites are blocked (Wiegers et al, 1997).…”

Expression and frameshifting but extremely inefficient proteolytic processing of the HIV-1 gag and pol gene products in stably transfected rodent cell lines

“…The major precursor to be expressed and processed in the HIV-infected cells is p55 (Mervis et a/., 1988). To show that the detected rp55 is identical to the viral GAG precursor, we have carried out further immunoblot analysis with rabbit hyperimmune sera to pl8 and p24 with extracts from p.gag-pol I-transfected cells.…”

“…Both precursor proteins of HIV-l are proteolytically processed with participation of the virus encoded protease. The GAG polyprotein gives rise to at least three components ~18, ~24, and pl5 (Mervis et al, 1988). The maturation of the GAG-POL polyprotein results in the release of the protease, the reverse transcriptase, and the integrase (Farmerie et a/., 1987;Lightfoote et a/., 1986;.…”

Major antigenic domain recognized by monoclonal antibodies maps within the carboxy‐terminal moiety of a recombinant human immunodeficiency virus‐1 p24 protein

“…1985; Mervis et al, 1988;Gottlinger et al, 19891. The interest of studying conformational and antigenic properties of p24 is relevant, as it represents a major B [Kitchen et al, 1984;Schupbach et al, 1984;Sarngadharan et al, 1984;Vilmer et al, 19841 and T cell [Walker et al, 1987;Nixon et al, 19881 target in immune response to HIV-1.…”