SUMMARYThe Marek's disease virus (MDV) homologue of the herpes simplex virus (HSV) gene encoding glycoprotein B (gB) has been identified within BamHI fragments 13 and K 3 of the 'highly oncogenic' strain RB 1B of MDV. The entire nucleotide sequence of the gene has been determined and its predicted amino acid sequence shown to share gross overall structural features with the gB genes of HSV, varicella-zoster virus (VZV) and other mammalian herpesviruses. In particular, all 10 cysteine residues were conserved in MDV gB and there was extensive homology throughout the gene with VZV, HSV and pseudorabies virus except for the N and C termini. The overall percentage amino acid identity between MDV gB and gB of the alphaherpesviruses had a mean of 50% which was almost twice that between cytomegalovirus and Epstein-Barr virus. Northern blot analysis showed that the main RNA transcribed from this gene is approx. 2.7 kb in size. Antibodies raised against synthetic peptides (residues 250 to 271 and 304 to 330) allowed the identification of a family of serologically related glycoproteins of Mr 110K, 64K and 48K in extracts of MDVinfected cells using immunoblots. Furthermore, the antisera were able to differentiate between the antigens of MDV and herpesvirus of turkeys in immunoblots. Immunofluorescence tests indicated that MDV gB is associated with granules in the cytoplasm and is present at the surface of MDV-infected cells.

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SUMMARYThe restriction endonuclease patterns of viral DNA obtained from serotypes 1 and 2 strains of Marek's disease virus have been compared and homology between the strains examined by hybridization. The results have shown that HPRS 16 (serotype 1) DNA has a structure similar to its attenuated variant HPRS 16/att except for a few fragments that are present only in the virulent strain. Evidence was obtained which suggested that these restriction fragments contained repeat sequences and that insertion of heterogeneous DNA occurred at these sites during attenuation of HPRS 16. The restriction enzyme patterns of HPRS 24 (serotype 2) differed substantially from those of HPRS 16 and HPRS 16/att and reassociation experiments showed that HPRS 24 shares less than 10 % homology with either H PRS 16 or herpesvirus of turkeys (serotype 3).Strains of Marek's disease virus (MDV) and herpesvirus of turkeys (HVT) have been divided into three types on serological grounds (Von Billow & Biggs, 1975a, b). Type 1 comprises pathogenic strains of MDV such as HPRS 16, GA and JM and their attenuated variants. Type 2 includes the naturally occurring non-pathogenic strain HPRS 24 and type 3 includes HVT. HPRS 24 differs from viruses of types 1 and 3 in having a lower growth rate in vitro and in forming'smaller plaques in chicken kidney cells (Biggs & Milne, 1972). Hirai et al. (1981) have recently reported a change in restriction endonuclease patterns of the serotype 1 strains GA and JM during attenuation. The purpose of this study was to compare the patterns obtained with HPRS 16, HPRS 16/att and HPRS 24 and in particular to study the homology between these strains, since little is known about the genetic relatedness of serotypes 1 and 2.The virus strains used were as follows: HPRS 16 (Purchase & Biggs, 1967), HPRS 16/att (Churchill et al., 1969), HVT strain FC126 (Witter et al., 1970) and HPRS 24 (Biggs & Milne, 1972). All virus strains were propagated in chick embryo fibroblasts (CEF) as cell-associated virus. HPRS 16 had been plaque-purified using virus derived from feather follicles of infected birds and was used within six passages in CEF. When inoculated into susceptible chickens, typical Marek's disease lesions were produced.The pathogenicity of HPRS 24 was investigated by inoculating Rhode Island Red chickens (HPRS RIR) with 1000 p.f.u, intra-abdominally. A score was given for lesions in peripheral nerves and in visceral organs and tissues as described previously (Biggs & Milne, 1972). In this system, lesions apparent to the naked eye were given a score of 5. Those chicks with no gross lesions were examined histologically and scores from 1 to 4 were given according to the severity of the lymphoid infiltration in the gonads and in the brachial, sciatic and coeliac plexuses. The scores for each chick in a group were added and a mean calculated. At 42 days after infection, 0/10 birds showed gross MD lesions in the group inoculated with HPRS 24 compared with 10/10 in the case of HPRS 16. Some birds infected with HPRS 24 showed mi...

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