Loss of Marek's disease virus tumorigenicity is associated with truncation of RNAs transcribed within BamHI-H.

The attenuation of Marek's disease virus (MDV) is associated with loss of pathogenicity and tumorigenicity. Previous studies have demonstrated a strong correlation between attenuation and amplification of a specific sequence located within the MDV terminal and internal repeats. We recently reported that the regions containing the amplified sequences, the BamHI D and H fragments, were transcriptionally active. However, differential transcription activity was observed to exist between attenuated and pathogenic MDV strains. Specifically, a major transcript of 1.8 kilobases was found to be produced by pathogenic MDV and not by attenuated MDV. We now report that the disappearance of this transcript is concomitant with the production of a 0.4-kilobase RNA, an RNA resulting from the truncation of the tumorigenicity-related transcript.