The post-translational maturation of the fusion protein (F) of human respiratory syncytial virus was investigated. Chemical cross-linking experiments indicated that F forms homotetramers and provided evidence that the intermonomer contacts involve primarily the F subunit. Homooligomerization as measured by sedimentation in sucrose gradients was insensitive to carbonyl cyanide -chlorophenylhydrazone, indicating that it occurs in the endoplasmic reticulum. Cleavage of the F precursor to yield the F and F subunits was blocked by monensin or brefeldin A, indicating that it takes place in distal cisternae of the trans Golgi compartment or in the more distal trans Golgi network. The F precursor was not detected at the cell surface in surface immunoprecipitation experiments, indicating that cleavage is intracellular. The appearance of the cleaved F protein at the cell surface was concurrent with that of the attachment glycoprotein (G); this and other information indicated that the type 2 membrane orientation of G is not obligatorily associated with a reduced transit rate. Examination of F maturation in the presence of tunicamycin provided evidence that its expression at the cell surface depends upon cleavage and not directly upon glycosylation.


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