IDENTIFICATION OF LATENCY-ASSOCIATED TRANSCRIPTS THAT MAP ANTISENSE TO THE ICP4 HOMOLOG GENE OF MAREKS-DISEASE VIRUS

Two small RNAs (0.9 and 0.75 kb), named Marek's disease virus (MDV) sm all RNAs (MSRs) and a 10-kb RNA, all of which map antisense to the MDV ICP4 homolog gene, have been readily detected in MDCC-MSB1 MDV-transf ormed T-lymphoblastoid cells. These RNAs were not detectable in reticu loendotheliosis virus-transformed T cells. When MDV was reactivated by treatment of lymphoblastoid cells with 25 mu g of iododeoxyuridine pe r mi, the relative levels of the transcripts decreased. These RNAs wer e not detected by Northern (RNA) hybridization in productively infecte d chicken embryo fibroblasts 48 h postinfection; however, they were ap parent 140 h postinfection. By using Northern hybridization, RNase pro tection assays, and primer extension analysis, the MSRs were determine d to map antisense to the predicted translational start site of the IC P4 homolog gene. The conclusion most consistent with the data is that the two MSRs are overlapping, spliced RNAs. Both small RNAs contain a latency promoter binding factor consensus recognition sequence located toward their 5' ends as well as two potential ICP4 recognition consen sus sequences, one in each orientation. The region contains a number o f small open reading frames on each side and within the MSRs. Although the exact endpoints are unknown, the large 10-kb species spans the en tire ICP4 homolog region. We believe that this group of RNAs, which ma p antisense to the ICP4 homolog gene, are latency-associated transcrip ts of MDV.