FURTHER CHARACTERIZATION OF THE LATENCY-ASSOCIATED TRANSCRIPTION UNITOF MAREKS-DISEASE VIRUS

Previous studies have identified a large (L) and a small (S) RNA trans cript antisense to the MDV homologue of the ICP4 gene of herpes simple x virus (HSV) in cells infected with Marek's disease virus (MDV) and i n lymphoblastoid cell lines. In this study the 5' and 3' ends of the L RNA and of the sense ICP4 transcript of MDV were mapped by Northern h ybridization and RNase protection assays. The results showed that L RN A is approximately 10.6 kb and that the ICP4 sense transcript is initi ated in the region of genomic DNA where the L RNA terminates whereas L RNA is initiated where the ICP4 transcript terminates. L RNA was abun dant in chick embryo fibroblasts (CEF) infected with virus strain HPRS 16/attenuated whereas S RNA was predominant in CEF infected with oncog enic HPRS16 and in RPL-1 cell line. Results of cycloheximide experimen ts showed that the ICP4 gene of MDV was transcribed as an immediate-ea rly gene in infected CEF whereas transcription of the L RNA required p rotein synthesis. Sequencing of cDNA and Northern hybridization using oligonucleotide probes showed that S RNA shared similar intron/exon bo undaries as the cDNAs from several cell lines indicating that there mi ght be a relationship between the S RNA and the antisense transcripts that generated the cDNAs.