Synthesis of mumps virus polypeptides in infected vero cells

Abstract

Mumps virus was adapted to growth in Vero cells, which yielded virus of high infectivity titers. The structural polypeptides of purified virions grown in Vero cells were similar to those described previously for egg-grown mumps virus: L (200K), HN (79K), NP (72K), F 1 (61K), P (45K), M (40K), and F 2 (16K). We have analyzed the synthesis of viral polypeptides in Vero cells by pulse labeling with radioactive amino acid precursors. The nucleoprotein (NP) was the first to be detected intracellularly above the cellular protein background at 6 h.p.i. By 12 h.p.i., all viral polypeptides were observed except for the glycoproteins F 1 and F 2, which are derived from a precursor designated F 0 (74K). Two low-molecular-weight polypeptides not present in purified virions were also detected in infected cells. They are designated pI (28K) and pII (19K). Peptide mapping revealed that these two polypeptides share regions of their amino acid sequence and that they are also related to the structural protein P. Polypeptides pI and pII were found in several cell types (Vero, CEF, MDBK cells) infected with mumps virus. Infection of Vero cells with other paramyxoviruses (SV5 and Sendai virus) did not induce the synthesis of proteins comparable to pI and pII, whereas in mumps virus-infected cells no counterpart to the nonstructural C protein of Sendai virus was detected. Pulse-chase experiments suggest that pI and pII may not be derived from P by proteolytic cleavage.