When 1-50-4 cells were infected with von Magnus virus derived from influenza AJRIJ5+ virus by four successive undiluted passages in chick embryos, virus-specific proteins were synthesized but production of infectious virus was inhibited. In these cells the synthesis of viral RNA was suppressed and the nucleoprotein (NP) antigen was found predominantly in the nucleus in contrast to standard virus-infected cells in which the antigen was distributed throughout the whole cell. The intracellular location and migration of NP were determined by isotope labeling and sucrose gradient centrifugation of subcellular fractions. In standard virus-infected cells NP polypeptide was present predominantly in the cytoplasm in the form of viral ribonucleoprotein (RNP) and intranuclear RNP was detected in reduced amounts. In contrast, in von Magnus virus-infected cells NP polypeptide was present predominantly in the nucleus in a non assembled, soluble form and the amount of cytoplasmic RNP was considerably reduced. After short-pulse labeling NP was detected exclusively in the cytoplasm in a soluble form and after a chase a large proportion of such soluble NP was seen in the nucleus. It is suggested that a large proportion of the NP synthesized in von Magnus virus-infected cells is not assembled into cytoplasmic RNP because of the lack of available RNA and the NP migrated into the nucleus and remained there.Canavanine, an arginine analog, is a potent inhibitor of the growth of influenza virus (11). It inhibits the synthesis of viral RNA and the formation of viral RNP.Under these conditions, most of the NP is found in the nucleus in a nonassembled, soluble form, in contrast to untreated cells in which a large amount of NP is distributed in the cytoplasm in the form of RNP. Influenza RNP consists of multiple molecules ofNP and one segment of virion RNA (vRNA) or cRNA complementary to vRNA (2, 17). We have suggested the possibility that the NP synthesized in the presence of canavanine is not assembled into cytoplasmic RNP because of the lack of available RNA and that the NP readily migrates into the nucleus and ac-1 Present address: Gamagori-Fukashi Hospital, Gamagori, Aichi 433.
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Host‐dependent restriction of influenza B virus replication in L cells was analysed in comparison with productive infection in MDCK or 1–5C‐4 cells. The synthesis and intracellular distribution of virus‐specific proteins and the production of cytoplasmic ribonucleoproteins in nonpermissive L cells were similar to those in permissive MDCK cells. However, an electron microscopic study of infected L cells showed neither extracellular virions nor budding virus particles on the cell surface, in contrast to MDCK cells which produced numerous virus particles. PAGE analysis of the plasma membrane isolated from the cells demonstrated no significant difference in the composition of viral polypeptides between permissive 1‐5C‐4 and nonpermissive L cells. It was noted that the abortiveness of influenza B virus infection in L cells may be due to a defect in host cell function involved in the initiation of virus budding.
When influenza A/RI/5+ virus-infected cells were incubated in medium to which 2 fig of canavanine (arginine analog) per ml had been added 4 hr after infection, all viral polypeptides were synthesized but the budding-like process with the appearance of extracellular virus was completely inhibited. The plasma membrane isolated from these cells contained exclusively hemagglutinin (HA), and membrane (M) protein and nucleoprotein (NP) appeared to be associated with the nucleus, in contrast to untreated cells whose plasma membrane contained abundant HA, M protein, and NP. Disruption of canavanine-treated cells by freeze-thawing generated a number of hemagglutinating membranous vesicles or fragments containing exclusively HA. By isotope labeling it was found that the M protein synthesized in the presence of canavanine, together with HA and NP, is a canavanine-substituted polypeptide. It is suggested that canavanine inhibits the formation of the mature envelope of influenza RI/5+, because of the inability of M protein to associate with the plasma membrane.
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