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.
1 Department of Veterinary Pathology, University of Liverpool, Leahurst, Neston, Cheshire CH64 7TE, UK
2 Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
Correspondence ...Clive J. Naylor cnaylor{at}liv.ac.uk
Avian pneumovirus (APV) is a member of the genus Metapneumovirus of the subfamily Pneumovirinae . This study describes the development of a reverse-genetics system for APV. A minigenome system was used to optimize the expression of the nucleoprotein, phosphoprotein, M2 and large polymerase proteins when transfected into Vero cells under the control of the bacteriophage T7 promoter. Subsequently, cDNA was transcribed from the virion RNA to make a full-length antigenome, which was also cloned under the control of the T7 promoter. Transfection of the full-length genome plasmid, together with the plasmids expressing the functional proteins in the transcription and replication complex, generated APV in the transfected cells. The recombinant virus was passaged and was identified by cytopathic effect (CPE) that was typical of APV, the presence of a unique restriction-endonuclease site in the cDNA copy of the genome and immunofluorescence staining with anti-APV antibodies. Replacement of the full-length wild-type antigenome with one lacking the small hydrophobic (SH) protein and the attachment (G) genes generated a virus that grew more slowly and produced atypical CPE with syncytia much larger than those seen with wild-type virus.
The GenBank/EMBL/DDBJ accession number for the APV genome sequence described in this study is AY640317 .
In order to understand the prevalence of hepatitis B virus (HBV) precore mutants isolated from asymtomatic carriers in Guangxi.
Nested polymerase chain reaction (nPCR) was used for amplification of ...HBV DNA precore in 77 carrier sera, followed by HBV DNA nPCR products sequencing using direct sequencing.
50.7% of 77 carriers was positive for HBV DNA with a prevalence of mutants 22.1% (17/77). HBV DNA positive rate in the southern part of the autonomous region was 55.6% (20/36). Six of them were mutants, counting for 30%. The common mutation in the southern part was seen T-->C at nt1858 while nt1896 stop mutation was discovered in one sample only, which was accompanied by point mutation at nt1837 (A-->G). HBV DNA positive rate in the northern part was 46.3% (19/41) with 11 of them were mutants, counting for 57.9%. The common mutation in that area stopped at nt1896. Among samples with stopped mutation, 4 samples had mutation at nt1846 (A-->T), 2 samples at nt1862 (G-->T). Both mutation at nt1856 (C-->T) and nt185
To explore the relationship between HBV core promoter mutations and liver damage or HBeAg status.
Nested polymerase chain reaction (nPCR) was used for amplification of HBV DNA core promoter in 59 ...sera from patients with chronic hepatitis B in Guangxi, then the HBV DNA positive products were sequenced by direct sequencing.
The HBV DNA positive rate of was 59.3%(35/59). All the patients were infected by mutants. The commonest mutation was the double mutation (A --> T at nt1762 and G --> A at nt1764), counting for 57.1% (20/35). The next was C --> G at nt1799, counting for 54.4% (19/35), but this was no function. A --> G at nt1752 (resulting in isoleucine to valine) was seen in 37.1% (13/35) of the HBV DNA positive patients, and T --> C at nt1753 was seen in 20% (7/35). The significant difference in the frequency of T1762A1764 mutant was found between HBeAg positive patients (31.3%) and negative patients (79.0%).
HBV core promoter mutations are common among patients with chronic hepatitis B in Guangxi. T1762A176
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