MUTATIONAL ANALYSIS OF THE FUSION PEPTIDE OF MOLONEY MURINE LEUKEMIA-VIRUS TRANSMEMBRANE PROTEIN P15E

Fusion peptides are hydrophobic sequences located at the N terminus of the transmembrane (TM) envelope proteins of the orthomyxoviruses and paramyxoviruses and several retroviruses. The Moloney murine leukemia virus TM envelope protein, p15E, contains a hydrophobic stretch of ami no acids at its N terminus followed by a region rich in glycine and th reonine residues, A series of single amino acid substitutions were int roduced into this region, and the resulting proteins were examined for their abilities to be properly processed and transported to the cell surface and to induce syncytia in cells expressing the ecotropic recep tor, One substitution in the hydrophobic core and several substitution s in the glycine/threonine-rich region that prevented both cell-cell f usion and the transduction of NIH 3T3 cells when incorporated into ret roviral vector particles were identified, In addition, one mutation th at enhanced the fusogenicity of the resulting envelope protein was ide ntified, The fusion-defective mutants trans dominantly interfered with the ability of the wild-type envelope protein to cause syncytium form ation in a cell-cell fusion assay, although no trans dominant inhibiti on of transduction was observed. Certain substitutions in the hydropho bic core that prevented envelope protein processing were also found. T hese data indicate that the N-terminal region of p15E is important bot h for viral fusion and for the correct processing and cell surface exp ression of the viral envelope protein.