SUMMARYThe rate of protein synthesis in chicken embryo cells infected with Sendal virus 18 to 20 h previously was about two times greater than in mock-infected controls. At this time of infection six stable virus-induced proteins, four major structural proteins (P, NH, NP and M) and two non-structural proteins (28K and 6IK), were identified by electrophoresis in SDS-polyacrylamide gel of total cell extracts. The structural glycopeptide F was not detected in the infected cell extracts. Pulse-chase experiments showed that P, NP, M and 28K proteins either did not undergo any post-translational processing or the processing occurred very rapidly. By contrast, a glycopeptide NH was apparently derived from one of two unstable precursors, 69K or 63K, which were revealed only after a short pulse. The synthesis of virus-specific proteins appeared to be regulated since its rate varied for individual classes of proteins.In nucleocapsid-like particles isolated from infected cells two major structural proteins (P and NP) were found. A minor component with a very large tool. wt. was revealed in these particles as well as in the virus particle.

Disulfide bonding in the major proteins of influenza virus A, WSN strain, was studied by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels under reducing and nonreducing conditions. The electrophoretic behavior of the proteins correlated with their localization in the virions and their chemical composition. The internal proteins of the viral particles, i.e. matrix and nucleoproteins, were shown to contain a relatively small number of cysteine residues. Electrophoresis under nonreducing conditions yielded multiple forms of the proteins which could be discriminated by small but readily observable, reproducible differences in their migration rates in the gel. The multiplicity of the protein forms was caused by the formation of intramolecular disulfide bonds in matrix and nucleoproteins that arose during or after solubilization in sodium dodecyl sulfate. On the other hand, we failed to detect native interand intramolecular linkages in matrix and nucleoproteins. External glycoproteins of the virions (HA and NA) had, in contrast to the internal ones, a higher number of cysteine residues and native disulfide bonds. At least three disulfide linkages were revealed in HA and NA in our experiments. In uncleaved HA all of the linkages were intramolecular. In NA at least one disulfide bond linked two identical polypeptides into a dimer. It was established that the reduction of the different disulfide linkages in HA and NA required different concentrations of the reducing agent.

Human immunodeficiency virus type 1 (HIV-1) chronically infected (CI) cell lines were established from HIV-1,~B/LA~-infected MT-4 cells that survived acute infection. The HIV env gene expressed in the two longterm cultured cell lines differed from that of the lines cultured for shorter periods, by coding for a glycoprotein gpl60 that had the C terminus deleted. One long-term cultured cell line, CI-17, was studied in detail. An insertion of a premature stop codon in the env gene caused about 90 % of gpl60 molecules to be truncated (gpl60x), lacking both cytoplasmic and transmembrane domains; these species were secreted into the cell medium, and could form oligomers with other truncated gpl60 molecules as well as with their normal counterparts. CI-17 cells constantly yielded high levels of viral protein and relatively low quantities of infectious virus, without cytopathicity. However, acute infection of fresh MT-4 cells with CI-17-derived virus led to cytopathicity, the rate of which as well as the Env glycoprotein pattern depended on multiplicity: (i) using an infection dose of 10 -4 IDs0/cell, cells died 7 to 8 days post-infection with normal gpl60 synthesis predominating; (ii) with l0 -2 IDs0, gpl60x was produced as early as 48 h postinfection and cell death was delayed. Predominant gpl60x formation occurred again when new CI cell lines were obtained with CI-17-derived virus. Thus, two human immunodeficiency virus variants, a normal and a defective one, are persistently expressed in CI-17 cells. The other long-term cultured CI cell line also expressed gpl60 with a similar (albeit slightly longer) deletion of a C-terminal region in most molecules, but the cell lines that were cultured for shorter periods did not. These results suggest that the emergence of HIV variants with a C-terminal deletion in the Env glycoprotein, which coexist with normal virus, may play a role in maintaining the long-term growth capacity and viability of CI ceils.

Protein content and localization of individual proteins of rabies virus have been studied. Four major proteins (estimated molecular weights, about 65,000, 54,000, 37,000 and 21,000), one minor component (molecular weight, about 200,000), and one intermediate (as regards its molar concentration) component (molecular weight, about 43,000) were revealed in rabies virus paarticles. In subviral particles accumulating in virus-infected cells, the 200,000-, 54,000-, and 37,000-dalton components were revealed. Some properties of the subviral particles allow them to be considered as viral nucleocapsids and the proteins composing them as analogs of L, N, and NS proteins of other rhabdoviruses. Thus, the protein composition of the rabies virus strain studied does not differ from that of other rhabdoviruses.

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