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The isolation of additional bacteriophages besides φ6 containing segmented double-stranded RNA genomes (dsRNA) has expanded the Cystoviridae family to nine members. Comparing the genomic sequences of these viruses has allowed evaluation of important genetic as well as structural motifs. These comparative studies are resulting in greater understanding of viral evolution and the role played by genetic and structural variation in the assembly mechanisms of the cystoviruses. In this regard, the large double-stranded RNA genomic segment of bacteriophage φ12 was copied as cDNA and its nucleotide sequence determined. This genome''s organization is similar to that of the large segment of bacteriophages φ6, φ8, and φ13. In the amino acid sequence of the viral RNA-dependent RNA polymerase (P2), similarity was found to the comparable proteins of φ6, φ8, and φ13. Amino acid sequence similarity was also noted in the nucleotide triphosphate phosphorylase (P4) to the comparable proteins of φ8 and φ13. [Copyright &y& Elsevier]

The isolation of additional bacteriophages containing segmented double-stranded RNA genomes has expanded the Cystoviridae family to nine members. Comparing the genomic sequences of these viruses has allowed evaluation of important genetic as well as structural motifs. These comparative studies are resulting in greater understanding of viral evolution and the role played by genetic and structural variation in the assembly mechanisms of the cystoviruses. In this regard, the small and middle double-stranded RNA genomic segments of bacteriophage φ12 were copied as cDNA and their nucleotide sequences determined. This genome''s organization is similar to that of the small and middle segments of bacteriophages φ6, φ8, and φ13. Although there is little similarity in the nucleotide sequences, similarity exists in the amino acid sequence of the lysis cassette proteins to those of φ6. The host cell attachment proteins are found to have marked similarity to the φ13 attachment proteins. [Copyright &y& Elsevier]

In an effort to simplify and expand the utility of African horse sickness virus (AHSV) reverse genetics, different plasmid-based reverse genetics systems were developed. Plasmids containing cDNAs corresponding to each of the full-length double-stranded RNA genome segments of AHSV-4 under control of a T7 RNA polymerase promoter were co-transfected in cells expressing T7 RNA polymerase, and infectious AHSV-4 was recovered. This reverse genetics system was improved by reducing the required plasmids from 10 to five and resulted in enhanced virus recovery. Subsequently, a T7 RNA polymerase expression cassette was incorporated into one of the AHSV-4 rescue plasmids. This modified 5-plasmid set enabled virus recovery in BSR or L929 cells, thus offering the possibility to generate AHSV-4 in any cell line. Moreover, mutant and cross-serotype reassortant viruses were recovered. These plasmid DNA-based reverse genetics systems thus offer new possibilities for investigating AHSV biology and development of designer AHSV vaccine strains. [ABSTRACT FROM AUTHOR]