Biosynthesis of Mumps Virus F Glycoprotein: Non-fusing Strains Efficiently Cleave the F Glycoprotein Precursor

Abstract

Mumps virus infection of the CV-1 cell line results either in no cytopathic effect or extensive cell fusion, depending upon the infecting mumps virus strain. Growth cycle analyses indicated that both types of infection were the result of multiple cycle replication of mumps virus. Intracellular virus-specific polypeptide synthesis was examined by pulse- and pulse-chase-labelling with radioactive amino acids and sugars. The major polypeptides seen on SDS-polyacrylamide gels were NP (69000 mol. wt.), P (45 000 mol. wt.) and M (40000 mol. wt.); a non-structural polypeptide (22000 mol. wt.) was also present in infected cell lysates. The HN (74000 to 79000 mol. wt.) glycopolypeptide was detected in [³H]glucosamine- and [³H]mannose-labelled infected cells. A 65000 mol. wt. species that had incorporated these precursors was seen in pulse-labelled infected cell lysates, and this glycopolypeptide vanished during the chase interval with the concomitant appearance of two glycopolypeptides (59000 mol. wt. and 14000 to 15000 mol. wt.) which represented the F₁ and F₂ subunits of the F glycoprotein. Immunological data confirmed the relatedness of the 65000 mol. wt. glycopolypeptide to the F glycoprotein and identified it as the precursor F₀. The F₀ precursor glycopolypeptide was seen in cells infected with both fusing and non-fusing strains, and F₀ was processed completely to F glycoprotein for all infections. Thus, the lack of cell fusion after infection with certain mumps strains is not the consequence of incomplete processing of the F₀ precursor.