The genome of a very virulent Marek's disease virus.
The first complete genomic sequence, with analysis, of a very virulent strain of Marek's disease virus serotype 1 (MDV1), Md5 was presented. The genome was 17 7874 bp and predicted to encode 103 proteins. MDV1 was colinear with the prototypic alphaherpesvirus herpes simplex virus type 1 (HSV-1) within the unique long (UL) region, and was most similar at the amino acid level to MDV2, herpesvirus of turkeys (HVT), and non-avian herpesviruses equine herpesviruses 1 and 4. MDV1 encoded 55 HSV-1 UL homologues together with 6 additional UL proteins that are absent in non-avian herpesviruses. The unique short (US) region was colinear with and had greater than 99% nucleotide identity to that of MDV1 strain GA. However, an extra nucleotide sequence at the Md5 US/short terminal repeat boundary resulted in a shorter US region and the presence of a second gene (encoding MDV097) similar to the SORF2 gene. MD5, like HVT, encoded an ICP4 homologue that contains a 900-amino acid amino-terminal extension not found in other herpesviruses. Putative virulence and host range gene products included the oncoprotein MEQ, oncogenicity-associated phosphoproteins pp38 and pp24, a lipase homologue, a CxC chemokine, and unique proteins of unknown function MDV087 and MDV097 (SORF2 homologues) and MDV093 (SORF4). Consistent with its virulent phenotype, Md5 contained only two copies of the 132-bp repeat which has previously been associated with viral attenuation and loss of oncogenicity. The MDV1 Md5 genome sequence was deposited in GenBank under accession number AF243438.