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Title: Studies on the replication and functions of Newcastle disease virus ribonucleic acids
Author: Meager, Anthony
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1972
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It was shown by sucrose density gradient centrifugation that NDV particles contain two RNA species, a single high molecular weight RNA species and heterogeneous low molecular weight RNA. The high molecular weight RNA species, which is the viral genome, had a sedimentation coefficient of approximately 50S, and a molecular weight of ~5 x 106 as determined by RNA polyacrylamide gel electrophoresis. The heterogeneous low molecular weight RNA, which was not examined, was probably comprised of degraded 50S RNA and contaminating cellular RNA, and had a sedimentation coefficient of 4S. Virus specific RNA isolated from NDV infected cells was shown by sucrose density gradient centrifugation to contain 4 main components, 50S, 35S, 22S and 18S RNAs. Resolution of the component RNA species of Newcastle Disease virus specific intracellular RNA (ND vsi-RNA) using sucrose gradients was poor, and it was later shown that this could be much improved using RNA polyacrylamide gel electrophoresis. Both the 22S and 18S size class RNAs of ND vsi-RNA were demonstrated to be heterogeneous by using polyacrylamide gel electrophoresis. The molecular weights of all the distinguishable RNA species contained in ND vsi-RNA were determined by calibration of the polyacrylamide gels with a range of RNA molecules of well characterised molecular weights, i.e. HeLa cell nucleolar RNA. A correlation between virus virulence and ND-vsi RNA synthesis, particularly of the l8S size class of RNA, was observed. The explanation of this correlation is not yet possible. The sub-genomic RNA species of ND vsi-RNA were found in association with chick polyribosomes implicating them as viral messengers. The general properties of NDV RNA-dependent RNA polymerase were investigated and found in the main to be in agreement with published results (Huang et al., 1971). This enzyme, contained in NDV particles, is probably responsible for the synthesis of sub-genomic, complementary RNA species found in NDV infected cells, although it was demonstrated that it did not synthesise these species in vitro It was found that different NDV strains had different polymerase specific activities, but no correlation with virus virulence was apparent. It was also shown that RNA polymerase activity of several NDV strains was unstable at 4º C and 37ºC. Polymerase activity was reduced at 4º C, but increased by incubation at 37º C. It was shown that polymerase activity was retained after removal of the viral envelope, comprising virus glycoproteins and phospholipid, suggesting that the viral envelope plays no part in determining polymerase activity. The protein(s) contained in the virus particles responsible for polymerase activity was not identified. NDV RNA polymerase activity and infectivity were shown to be destroyed by ultra-violet irradiation and the virucide, β-propiolactone. NDV inactivated by ultra-violet irradiation or β-propiolactone was a good inducer of interferon in chick cells. The retention of some RNA polymerase activity in inactivated NOV particles suggested that this enzyme might have a role in the induction of interferon formation. Further investigations using NOV inactivated in various ways, e.g. heat at 5S o C, has strengthened this idea (Sheaff et al., 1972).
Supervisor: Not available Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QR355 Virology