RESUMEN
Sequence analysis of the nucleoprotein and phosphoprotein (P) genes of viruses in the hamster neurotropic lineage of measles virus revealed that the neurotropic variants are quite different from the Philadelphia 26 progenitor strain. In Vero cells persistently infected with the hamster neurotropic strain, predicted changes occur in 5.0% of the nucleoprotein and 8.1% of the P amino acids and some of these changes appear to affect the relative electrophoretic mobility of each protein. To evaluate one aspect of the viral polymerase complex containing these mutations, the distribution of P mRNA editing in each of the three strains was determined by both cloning and sequencing of polymerase chain reaction-amplified DNA fragments which included the editing site and by primer extension analysis of viral mRNA. Editing of P mRNA in the neurotropic strains shows a shift away from the single G insertion product to those with greater than 2 Gs inserted. The altered editing distribution has implications for the role of transcriptional regulation in measles virus persistence.
Asunto(s)
Virus del Sarampión/genética , Virus del Sarampión/metabolismo , Mutación , Fosfoproteínas/genética , Edición de ARN , Proteínas Virales/genética , Animales , Encefalopatías/etiología , Chlorocebus aethiops , Clonación Molecular , Cricetinae , Genes Virales , Sarampión/etiología , Virus del Sarampión/patogenicidad , Datos de Secuencia Molecular , ARN Mensajero/metabolismo , ARN Viral/metabolismo , Células VeroRESUMEN
Vero cells persistently infected with the hamster neurotropic strain (HNT-PI) of measles virus are deficient in the release of extracellular virus and syncytia formation, suggesting that mutations occur within the viral envelope proteins. Nucleotide sequence comparisons indicated that the coding regions of the matrix (M) and fusion (F) genes of HNT-PI were relatively conserved compared with those of their lytic progenitor virus Philadelphia 26 (Ph26), whereas the hemagglutinin (H) gene differed by 4.2% at the amino acid level. Northern blot analyses demonstrated the predominance of bicistronic M/F transcripts in HNT-PI at a 5:1 ratio over F monocistronic mRNA. Accordingly, no F protein could be detected in the HNT-PI cell line, although both the M and H proteins were produced in amounts comparable to those of Ph26. When the Semliki Forest virus replicon was used, coexpression of the HNT-PI F and Ph26 H genes resulted in the formation of multinucleated syncytia in transfected Vero cell cultures. Since the HNT-PI F protein was fusogenic, the restriction of its monocistronic mRNA is postulated to be a contributing factor in the reduction of cell fusion and ultimately in the maintenance of the persistent infection.
Asunto(s)
Virus del Sarampión/crecimiento & desarrollo , Panencefalitis Esclerosante Subaguda/microbiología , Proteínas Virales de Fusión/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Fusión Celular , Clonación Molecular , Regulación Viral de la Expresión Génica , Datos de Secuencia Molecular , ARN Mensajero/genética , Células Vero , Proteínas Virales de Fusión/química , Latencia del VirusRESUMEN
To characterize the genetic properties of currently circulating strains of wild-type measles viruses, we constructed and sequenced cDNA clones of the nucleoprotein (N) and matrix (M) genes of wild-type strains isolated between 1958 and 1989. The N and M genes of wild-type isolates from the prevaccine era (before 1964) were highly related to each other and to the N and M genes of a currently used measles vaccine strain, Moraten. The N and M genes of these viruses differed by no more than 0.5% at the nucleotide level. In contrast, the N and M genes of wild-type viruses isolated between 1977 and 1989 showed genetic drift, with the greatest amount of drift occurring in the viruses isolated from recent cases in the United States. Overall, the M genes were slightly more conserved at the nucleotide level (2.6% nucleotide, 3.3% amino acid) than the N genes (4.8% nucleotide, 3.4% amino acid). Alignment of the predicted protein sequences of the N genes revealed two regions of amino acid heterogeneity. The evolutionary patterns for the N and M genes suggested that the wild-type viruses isolated in the United States in 1989 were more related to wild-type viruses isolated in the United Kingdom between 1983 and 1988 than to viruses isolated in the United States in 1983.