The structure of Marek disease virus DNA: the presence of unique expansion in nonpathogenic viral DNA.

DNA of Marek disease virus (MDV) consists of two unique regions UL and US flanked by long inverted repeat regions TRL and IRL, and short inverted repeat regions TRS and IRS, respectively, similar to herpes simplex virus DNA. Comparison of restriction patterns between pathogenic and nonpathogenic MDV DNA was made to identify a region of viral DNA different between these two types of MDV, as it may be responsible for the tumorigenicity of MDV in chickens. The results indicated that BamHI-D and -H, located at the long inverted repeat regions TRL and IRL, were specifically expanded in nonpathogenic viral DNA. The location of the expanded region has been determined within 1.5 kilobase pairs of the Bgl I/Pst I fragment of BamHI-D and -H, close to the junction between the inverted repeat and the unique region. The possibility that a gene responsible for tumor induction may be disrupted by such expansion has been discussed.