Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 4, 2008
Publication Date: June 20, 2008
Citation: Spatz, S.J., Rue, C.A. 2008. Sequence determination of a mildly virulent strain (CU-2) of Gallid herpesvirus type 2 using 454 pyrosequencing. Virus Genes. 36:479-489. Technical Abstract: The complete DNA sequence of the mildly virulent Gallid herpesvirus type 2 strain CU-2 was determined and consists of 176,922 bp with an overall gene organization typical of class E alphaherpesviruses. Phylogenetically, this strain partitions in its own branch between the virulent strains RB-1B, Md11 and Md5, and the vaccine strain CVI988. Overall the genome of CU-2 is more similar to that of CVI988, with identically sized unique short regions of 11,651 bp. As in CVI988, an insertion of 177 bp was identified in the overlapping genes encoding the MEQ, RLORF6 and 23 kDa proteins within the repeat long region of the genome. A total of 15 single nucleotide polymorphisms (SNPs) common to both CU-2 and CVI988, and not occurring in virulent strains, were identified in the genes encoding UL29, UL45, UL50, UL52, LORF10, RLORF14a, RLORF12, MEQ(RLORF7), 23kDa, ICP4, US3 and two hypothetical proteins MDV071.4 and MDV076.4. Two SNPs were identified in the genes encoding UL29 and MEQ. Only one major open reading frame (ORF) encoding UL41, the virus host shutoff (VHS) ribonuclease, was disrupted in the CU-2 genome. An additional cytosine after the 25 codon is predicted to produce a truncated protein of 97 aa. Since GaHV-2 mutants lacking UL41 have been reported to retain their virulence, other factors are likely responsible for the low virulence of CU-2. It is largely suspected that SNPs in common with CVI988 along with the insertions in the MEQ loci are responsible for its phenotype. Conversely, we identified 43 nonsynonymous mutations (within 23 genes) that may contribute to the virulence of CU-2. These SNPs are shared exclusively with all sequenced virulent strains (Md5, Md11 and RB-1B) and not present within the CVI988 genome. Although most occur in proteins of unknown function, a significant percentage are in proteins involved in virion assembly.