- Volume 45, Issue 3, 1979

The time course of the synthesis of cucumber mosaic virus (CMV), CMV coat protein and the four CMV RNAs has been followed in cowpea protoplasts. CMV synthesis was estimated by analytical sucrose gradient centrifugation of extracts from protoplasts and by infectivity assay; coat protein synthesis was determined by incorporation of radioactive amino acids and analytical polyacryl-amide slab gel electrophoresis, while the synthesis of CMV RNAs was determined by hybridization analysis with labelled specific complementary DNA (cDNA) probes. There was a co-ordinate synthesis of CMV, CMV coat protein and virus RNA up to 50 h p.i. whereas the rate of coat protein synthesis reached a peak at about 15 h p.i. Coat protein was the only virus-induced protein detected. Results on the relative synthesis of RNAs 3 and 4 indicated that RNA 4 was derived by nucleolytic cleavage of RNA 3 and not by transcription of a negative RNA 4 strand.

Tracheal organ cultures were prepared from strains of mice with known susceptibility to the lethal effects of mouse cytomegalovirus. When organ cultures from susceptible mice were infected with this virus, characteristic c.p.e. developed and virus titres > 105 p.f.u./ml were produced 2 to 3 weeks after infection. Identically infected tracheal organ cultures from resistant mice consistently failed to develop significant virus c.p.e. and produced 10- to 100-fold lower titres of virus. When fibroblast cultures were infected with mouse cytomegalovirus, however, no consistent differences between susceptible and resistant mouse strains were observed. Since cytomegalovirus replicates in epithelial cells both in vivo and in tracheal organ culture, these results suggest that resistance may be based in part upon innate genetic susceptibility of epithelial cells to cytomegalovirus infection.

The neuraminidase activity of two strains of Duck/Mississippi/75 virus: DK/Mississippi/320 and DK/Mississippi/334 was studied. These neuraminidases hydrolyse the α 2→3 and α 2→8 ketosidic bonds of different substrates such as fetuin, N-acetyl neuramine lactose and colominic acid, but do not hydrolyse the α2→6 bonds of mucin type I and type II. The kinetic values of the neuraminidases, Michaelis constant, maximal and initial velocities and the effect of pH, temperature and detergents were also evaluated. The isolates differ mainly in the optimal pH and temperature conditions of activity. As with other paramyxovirus neuraminidases, the enzyme of DK/Mississippi/75 was destroyed by ionic but not non-ionic detergents.

The haemagglutinin of A/Dk/Alb/60/76, an influenza A virus isolated from feral ducks in Canada, possesses no antigenic relatedness to any of the 16 reference haemagglutinin subtypes. Results of serological tests (HI and double immuno-diffusion) with monospecific antisera to the haemagglutinin of this virus indicate that it represents a new avian haemagglutinin subtype. We propose that this haemagglutinin be designated as Hav10 under the current system of nomenclature.

The constituents of LS antigen from cells infected with vaccinia virus and with cowpox virus were compared by immunoprecipitation and SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Antiserum to the LS antigen from cells infected with vaccinia virus reacted with at least five polypeptides in cells infected with either virus. Four of these polypeptides were similar sizes in cells infected with the two viruses. However, one major polypeptide with a mol. wt. of about 100000 (100 K) detected in cells infected with vaccinia virus was not found in cells infected with cowpox virus. Conversely, a polypeptide with a mol.wt. of about 60000 (60K) was detected only in cells infected with cowpox virus.

Antibody produced against preparations of VP1, one of the four structural polypeptides of foot-and-mouth disease virus, neutralized the virus and reacted with both full and empty particles in radioimmunoassays (RIA). Antiserum against VP2 reacted with artificial empty particles of the virus but not with full particles. In contrast, none of the individual polypeptides of poliovirus produced antisera which neutralized the virus nor reacted with it in RIA. However, antisera produced with VP1 and VP2 reacted with artificial empty particles in RIA.

The disposition of chromosome proteins about the endogenous proviral DNA of BALB-c mouse has been studied. The sensitivity of the endogenous proviral DNA sequences to deoxyribonuclease I (DNaseI) was analysed in BALB-c mouse tissues (liver and spleen) and in the cell line JLS-V9 which does not produce virus. On all of these preparations the endogenous proviral DNA was as sensitive to DNase I digestion as total chromatin. Since the proviral genes in JLS-V9 cells were silent, it was of interest to study possible changes in the chromatin structure following virus induction by iododeoxyuridine. We could not detect any increase in the sensitivity of the endogenous proviral DNA to DNase I digestion following induction. The induction was very efficient, however, since 60% of the cells responded to produce intracellular virus antigens.