The structural proteins of Newcastle disease virus. I. Identification of a minor internal protein

The structural polypeptides of avian paramyxoviruses

The structural polypeptides of twenty-three avian paramyxoviruses from five serotypes were examined by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate under reducing and non-reducing conditions. All virus polypeptide profiles consisted of 7--10 polypeptides of which two were glycosylated. Some variation was seen in the profiles of viruses from the same serotype, but groups formed on the basis of their serological relationships in haemagglutination inhibition tests were identical to those formed on the basis of similarities in their polypeptide profiles.

Isolation and characterization of heat-resistant (HR) mutants of Newcastle disease virus

Heat-resistant (HR) mutants (MR 70 and HR 74) of Newcastle disease virus (NDV) which exhibited significantly higher thermostability in their infectivity than wild-type virus were isolated and characterized. They differ from each other in their plaque morphology; HR 70 produces small turbid plaques, whereas those of HR 74 are large and clear. Cytopathogenicity of these mutants is much lower than that of the wild-type virus in cultured cells such as CEF, LLCMK2 and HeLa cells. Moreover, these HR mutants exhibited extended mean embryo survival times. Synthesis of cellular RNA's and proteins in cells infected with HR mutants was not significantly reduced under conditions in which synthesis of these macromolecules was strongly reduced in cells infected with wild-type virus. No significant differences were observed between HR mutants and wild-type virus in their other phenotypic characteristics such as the capacity for interferon production, growth characteristics at a low multiplicity of infection, and cleavage of viral glycoproteins in infected cells. From these findings, it was suggested that the inhibitory effect of virus infection on cellular macromolecular synthesis is a possible determinant of cytopathogenicity of NDV.

Intracellular development of membrane protein of influenza virus

The intracellular development of membrane protein (MP) of influenza A virus was investigated by immunofluorescent staining. Monospecific antiserum was prepared by immunizing rabbits with MP eluted from SDS-polyacrylamide gels of SDS-disrupted NWS virions. In the productive infection in clone 1-5C-4 cells, MP antigen was first detected over the whole cell at 4 hr after infection, concomitantly with the appearance of hemagglutinin (HA) antigen in the cytoplasm, and bright nuclear fluorescence was then observed. Nucleoprotein (NP) antigen was detected in the nucleus prior to the appearance of fluorescence of MP antigen and thereafter the cytoplasmic fluorescence developed. Late in infection, all of these three antigens were observed predominantly in the cytoplasm with stronger fluorescence at the cell surface. Essentially similar findings were obtained in the abortive infections in L cells and BHK cells. The above results suggest that the membrane protein of influenza A virus is present in the nucleus as well as in the cytoplasm of infected cells.

Polypeptides of respiratory syncytial virus

Radiolabeled respiratory syncytial virus was purified from medium that had been harvested from infected HeLa cell monolayers before it contained much cellular debris. After isopycnic centrifugation in linear gradients prepared with sucrose dissolved in Hanks balanced salt solution, almost all the infectivity and most of the radioactivity were recovered in a single band with density from 1.16 to 1.23 g/cm3 and a peak at 1.2 g/cm3. Analysis by polyacrylamide gel electrophoresis resolved the purified virus into seven polypeptides of approximate molecular weights 20,000 to 80,000, of which the two largest and the smallest proved to by glycoproteins.

Recovery of infectious proviral DNA from mammalian cells infected with respiratory syncytial virus

The DNA fraction from a line of bovine embryonic kidney cells originally exposed as primary cultures several months earlier to a temperature-sensitive (ts) mutant of respiratory syncytial (RS) virus could be used to transfect human HEp-2 cells with the production of infectious RS virus. The DNA donor cells, designated BEK/RS ts, retained their healthy fibroblastic appearance during continuous cultivation at a temperature (39 degrees) restrictive for growth of the original infecting mutant and showed no evidence for RS virus replication or viral antigen synthesis when directly examined for these activities by conventional methods. The infectious property of the DNA from BEK/RS ts cells was abolished by exposure of the nucleic acid preparation to DNase (but not RNase) or by pretreatment of recipient HEp-2 cells with actinomycin D or mitomycin C. The latter drug treatments substantially enhanced the replication of infecting wild-type RS virus in HEp-2 cells. Viral isolates derived from the progeny of a DNA transfection included clones possessing several genetic markers of the RS ts mutant originally used to infect BEK/RS ts cells and other virus clones that appeared to be either hybrid or wild-type for phenotypic properties such as their temperature sensitivity. An infectious proviral DNA was also detected in a line of virogenic HEp-2 cells (HEp-2/RS) persistently infected with respiratory syncytial virus after exposure to the wild-type strain 2 years earlier.