Nature of transient inhibition of deoxyribonucleic acid synthesis in HeLa cells by parainfluenza virus 1 (Sendai)

Adsorption of ultraviolet-inactivated Sendai virus, at high or low multiplicity, to HeLa cells caused a transient increased incorporation of (3)H-thymidine into the cellular deoxyribonucleic acid (DNA). In HeLa cells synchronized by a double-thymidine block, this increased incorporation of thymidine during the S phase lasted from about 30 to 90 min after virus adsorption. The observations that the kinetics of accumulation of radioactive thymidine in the nucleotide pool did not differ in control and in the virus-treated cells and that the (32)P incorporation into the DNA of the virus-treated cells was inhibited at the same time indicate that the augmented incorporation of (3)H-thymidine into DNA results from a transient block in the endogenous pathway of thymidine synthesis. Chromatographic analysis of the nucleotide pool of the virus-treated cells labeled with (14)C-formate indicates that methylation of deoxyuridine monophosphate to thymidine monophosphate is inhibited. It is suggested that the inhibition is caused by a block of either the thymidilate synthetase or some step in the tetrahydrofolate cycle.

Cell fusion by various strains of Newcastle disease virus and their virulence

Some properties of eight strains of Newcastle disease virus (cell-fusing ability, hemolysin, heat stability of hemagglutinin or of hemolysin) do not correlate with virulence of these strains.

Electron Microscopic Study of Penetration of Newcastle Disease Virus into Cells Leading to Formation of Polykaryocytes

Treatment of FL or Lu 106 epithelial cells with Newcastle disease virus (NDV) at an input multiplicity of 500 EID50 per cell induces in these cells the formation of polykaryocytes at the end of 2-3 h of contact. Electron micrographs of such NDV-treated monolayers after 2-10 min of incubation show the presence of virions adsorbed to the cell membranes, in vacuoles and with the viral envelope partly fused with the cell membrane. In polykaryocytes induced by NDV, remnants of cell membranes showing numerous breaks may still be present after 3 h.

Thrombocytopenia in Guinea Pigs Infected by Encephalomyocarditis Virus (EMC)

Intraperitoneal infection of guinea pigs with Encephalomyocarditis (EMC) virus led to viremia 2-10 days after infection and to paralysis and death of some of the infected animals. During the course of infection there was marked leucocytosis and thrombocytopenia. No abnormalities were detected in megakaryocytes in bone marrow cultures from infected guinea pigs. Exposure of guinea pig bone marrow culture to EMC virus in vitro impaired granulation and disintegration of megakaryocytes to platelets.