Avian metapneumovirus SH gene end and G protein mutations influence the level of protection of live-vaccine candidates.
A prototype avian metapneumovirus (AMPV) vaccine (P20) was previously shown to give variable outcomes in experimental trials. Following plaque purification, three of 12 viruses obtained from P20 failed to induce protection against virulent challenge, whilst the remainder retained their protective capacity. The genome sequences of two protective viruses were identical to the P20 consensus, whereas two non-protective viruses differed only in the SH gene transcription termination signal. Northern blotting showed that the alterations in the SH gene-end region of the non-protective viruses led to enhanced levels of dicistronic mRNA produced by transcriptional readthrough. A synthetic minigenome was used to demonstrate that the altered SH gene-end region reduced the level of protein expression from a downstream gene. The genomes of the remaining eight plaque-purified viruses were sequenced in the region where the P20 consensus sequence differed from the virulent progenitor. The seven protective clones were identical, whereas the non-protective virus retained the virulent progenitor sequence at two positions and contained extensive alterations in its attachment (G) protein sequence associated with a reduced or altered expression pattern of G protein on Western blots. The data indicate that the efficacy of a putative protective vaccine strain is affected by mutations altering the balance of G protein expression.
Naylor
Clive J
CJ
Department of Veterinary Pathology, University of Liverpool, Leahurst, Neston, Cheshire, UK.
Ling
Roger
R
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
Edworthy
Nicole
N
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
Savage
Carol E
CE
Department of Veterinary Pathology, University of Liverpool, Leahurst, Neston, Cheshire, UK.
Easton
Andrew J
AJ
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D004195:Disease Models, Animal; D016679:Genome, Viral / Q000235:genetics; D029121:Metapneumovirus / Q000235:genetics* / Q000276:immunology* / Q000472:pathogenicity; D008969:Molecular Sequence Data; D009154:Mutation; D018184:Paramyxoviridae Infections / Q000276:immunology / Q000517:prevention & control; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012367:RNA, Viral / Q000096:biosynthesis / Q000235:genetics; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic; D014422:Turkeys; D014764:Viral Proteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D014765:Viral Vaccines / Q000235:genetics / Q000276:immunology*; D014774:Virulence / Q000235:genetics*
D012333:RNA, Messenger; D012367:RNA, Viral; D014764:Viral Proteins; D014765:Viral Vaccines