Epstein Barr virus specific RNA. I. Analysis of viral RNA in cellular extracts and in the polyribosomal fraction of permissive and nonpermissive lymphoblastoid cell lines

The authors analyzed the viral RNA in permissive and non permissive Epstein Barr virus (EBV) infected lymphoblastoid cell lines by observing the kinetics of hybridization of labeled EBV HR-1 DNA with unlabeled RNA extracted from whole cells or from the polyribosomal fraction. The data indicate the following: RNA, homologous to only 3% of the EBV HR-1 DNA, is present in the polyribosomal fraction of the nonpermissive Namalwa and Kurgans cells, suggesting that the function of only a small fraction of the EBV genome is required for the expression of the EBV related intranuclear antigen and to maintain lymphoblastoid cells in a transformed state. In general, the extent of the viral DNA sequences transcribed into stable RNA correlates with the extent of phenotypic expression of the EBV genome. RNA extracted from virus producing HR-1 cells contains RNA sequences transcribed from at least 45% of the viral DNA, whereas the nonpermissive cell lines contain transcripts homologous to a much smaller proportion of the EBV DNA. Viral RNA sequences found in the polyribosomal fraction of HR-1 cells arise from almost the same template as the viral RNA sequences in extracts of unfractionated HR-1 cells. In contrast, in nonpermissive lymphoblastoid cells, less than 30% of the viral RNA species found in whole cell extracts can be identified in the polyribosomal fraction. The authors interpret these observations to indicate that the expression of EBV genetic information is regulated in at least 2 ways: first, by some mechanism that regulates which DNA sequences give rise to stable RNA; second, through a mechanism whereby certain viral RNA transcripts are selectively excluded from stable association with the polyribosomes.