No abstract

The amino acid sequence at the F2/F1 cleavage site was determined for 15 strains of the so-called pigeon PMV-1 (PPMV-1) variant of Newcastle disease virus (NDV) which showed close antigenic identity, determined by their reactions with a panel of 28 monoclonal antibodies, but considerable variation in their pathogenicity for chickens. Thirteen of the isolates possessed the motif 112G-R-Q-K-R-F117. This motif was seen for one virus which had initially low pathogenicity and remained unaltered when virulence of the virus for chickens was increased by bird to bird passage. The two other viruses had the sequence 112R-R-Q-K-R-F117 at the cleavage site which is more typical of virulent viruses, however, pathogenicity index tests indicated that these isolates were of moderate and low pathogenicity. The nucleotide sequence coding for the HN/HN0 extension region was determined for two of the PPMV-1 isolates. In both cases a stop codon was present indicating that the product for these viruses would be HN571. We conclude that the wide variation in pathogenicity of the variant PPMV-1 for chickens is not related to variation in the amino acid motif at the F2/F1 cleavage site nor due to production of HN0 which may also influence pathogenicity. The high virulence of some of the viruses examined confirms that a double pair of basic amino acids in the region of the F2/F1 cleavage site is not necessary for the full expression of virulence.

Background: Most methods for constructing aneuploid yeast strains that have gained a specific chromosome rely on spontaneous failures of cell division fidelity. In Saccharomyces cerevisiae, extra chromosomes can be obtained when errors in meiosis or mitosis lead to nondisjunction, or when nuclear breakdown occurs in heterokaryons. We describe a strategy for constructing N+1 disomes that does not require such spontaneous failures. The method combines two well-characterized genetic tools: a conditional centromere that transiently blocks disjunction of one specific chromosome, and a duplication marker assay that identifies disomes among daughter cells. To test the strategy, we targeted chromosomes III, IV, and VI for duplication.

SUMMARYAvian influenza virus isolate A/mandarin duck/Singapore/805/F-72/7/93 was found to be consistently highly pathogenic by recognised in vivo testing procedures although it was of a subtype (H10) not usually associated with high pathogenicity. The virus was also not typical of highly pathogenic influenza viruses in that it was not pathogenic when administered intra-nasally, did not possess a haemagglutinin cleavage site with multiple basic amino acids and did not replicate in the brains of chickens after intravenous inoculation. A re-examination of the earlier H10 isolate A/turkey/England/384/79 suggested that it was similarly pathogenic. The pathogenicity may have been associated with replication in the kidney.

The nucleotide sequences of the entire F genes of two isolates of the pigeon PMV-1 (PPMV-1) variant of Newcastle disease virus (NDV) were determined using RTPCR. The deduced amino acid sequences of the F0 protein showed four differences between isolate 760/83 which had been passaged 4 times in chickens and gave an intravenous pathogenicity index in chickens (IVPI) of 2.01 and isolate 1168/84 which had received six passages in chickens and had an IVPI of 0.00. The F genes of virus from two passage levels of isolate 1447/84, 0 with IVPI value 0.00 and six with IVPI value 0.58, were partially sequenced to cover the areas of variation between 760/83 and 1168/84. The two passage levels of 1447/84 showed identical sequences in these areas which in turn were identical of those of 760/83. It was concluded that the recorded differences in intravenous pathogenicity were unlikely to be associated with differences in the primary structure of the F0 protein. Phylogenetic comparisons of the F gene sequences of the two PPMV-1 viruses with those published for other NDV strains and isolates showed that the PPMV-1 viruses formed a new fourth lineage but were closely related to strain Warwick with which they presumably shared a common origin.