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Title: Comparative Full Length Sequence Analysis of Oncogenic and Vaccine (Rispens) Strains of Marek's Disease Virus

item Spatz, Stephen

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/15/2006
Publication Date: 12/3/2006
Citation: Spatz, S.J., Petherbridge, L., Zhao, Y., Nair, V. 2006. Comparative Full Length Sequence Analysis of Oncogenic and Vaccine (Rispens) Strains of Marek's Disease Virus. Proceedings of 87th Conference for Research Workers in Animal Diseases. p. 166.

Interpretive Summary:

Technical Abstract: The complete DNA sequence of the Marek’s disease virus serotype 1 vaccine strain CVI988 was determined and consists of 178,311 bp with an overall gene organization identical to that of the oncogenic strains. In examining open reading frames (ORFs), nine ORFs differ between vaccine and oncogenic strains. A 177-base pair insertion was identified in the overlapping genes encoding the Meq, RLORF6 and 23 kD proteins of CVI988. Three ORFs are predicted to encode truncated proteins. One, designated 49.1, overlaps the gene encoding the large tegument protein UL36 and encodes a severely truncated protein of 34 aa. The others, ORF5.5/ORF75.91 and ORF3.0/78.0, located in the repeat regions (diploid), encode a previously unidentified ORF of 52 aa and a truncated version of the virus-encoded chemokine (vIL8), respectively. Subtle genetic changes were identified in two ORFs encoding tegument proteins UL36 and UL49. Only one diploid ORF (ORF6.2/ORF75.6) present in the genomes of the three virulent strains is absent in the CVI988-BAC genome. Seventy non-synonymous amino acid substitutions were identified that could differentiate CVI988-BAC from all three oncogenic strains collectively. Estimates of the non-synonymous to synonymous substitution ratio (omega) indicate that CVI988 ORFs generally are under purifying selection (omega <1), while UL39, UL49, UL50, RLORF6 and RLORF7 (Meq) appear to evolve under relaxed selective constraints. No CVI988 ORF was found to be under positive evolutionary selection (omega >>1). Consistent with its attenuated phenotype, CVI988 contains 14 copies of the 132-bp repeat that has previously been associated with viral attenuation and loss of oncogenicity.