UNSPECIFIED. (1993) GENOMIC CONCATEMERIZATION/DELETION IN ROTAVIRUSES - A NEW MECHANISM FOR GENERATING RAPID GENETIC CHANGE OF POTENTIAL EPIDEMIOLOGIC IMPORTANCE. JOURNAL OF VIROLOGY, 67 (11). pp. 6625-6632. ISSN 0022-538X

Abstract

Three variants of group A rotavirus with large changes in their gene 5 structures have been analyzed at the molecular level. The first of these, P9DELTA5, was obtained during plaque purification undertaken as part of the biological cloning of a field isolate of virus. The gene 5 homolog in this isolate migrated just ahead of the normal segment 6 RNA, giving an estimated size of 1,300 bp. Molecular cloning and sequencing of this homolog revealed it to have a single 308-bp deletion in the center of the normal gene 5 sequence extending between nucleotides 460 and 768 of the normal gene sequence. This deletion caused a frameshift in the gene such that a stop codon was encountered 8 amino acids downstream of the deletion point, giving a predicted size for the protein product of this gene of 150 amino acids compared with the 490 amino acids of its normal-size counterpart. Attempts to detect this shortened protein in virus-infected cells were not successful, indicating that it was much less stable than the full-length protein and/or had suffered a large change in its antigenicity. The second two variants, brvA and brvE, were generated in an earlier study following the high-multiplicity passage of the UKtc strain of bovine rotavirus. Polyacrylamide gel electrophoresis analysis of these nondefective variants showed that brvA had a gene 5 homolog approximately equal in size to the normal RNA segment 2 (approximately 2,700 bp) and that brvE had a size of approximately 2,300 bp. Both variants showed changes in their gene 5 protein products, with brvA mimicking P9DELTA5 in failing to produce a detectable product whereas brvE produced a new virus-specific protein approximately 80 kDa in size. Full-length cDNA clones of the brvE gene 5 homolog were isolated, and analysis of their structure revealed a head-to-tail concatemerization of the normal gene 5 sequence with the first copy of the concatemer covering nucleotides 1 to 808 and the second covering nucleotides 92 to 1579, giving a total length of 2,296 bp. Sequencing across the junction region of the two copies of the gene showed that they were joined in frame to give a predicted combined open reading frame of 728 amino acids with the amino-terminal region consisting of amino acids 1 to 258 fused at the carboxy terminus to amino acids 21 to 490. The biological phenotypes, in terms of virus yield and plaque size, of brvA and brvE were compared with those of the parent UKtc strain. This showed that both variants gave a somewhat reduced virus yield and that brvE had plaques covering an average 2.5-fold smaller area whereas brvA gave plaques whose area was reduced by approximately 50-fold. These results demonstrate that in rotaviruses rapid genomic change through both deletion and concatemerization can generate nondefective virus variants whose protein coding potential has been altered, leading to changes in biological phenotype. This new mechanism for effecting rapid genomic change has now to be considered one by which rotaviruses are able to rapidly change the nature of the proteins they encode, which may in turn lead to important epidemiological changes.

Data sourced from Thomson Reuters' Web of Knowledge

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