REGULATION OF THE DOUBLE-STRANDED RNA-DEPENDENT PROTEIN-KINASE PKR BYRNAS ENCODED BY A REPEATED SEQUENCE IN THE EPSTEIN-BARR-VIRUS GENOME

During the initial infection of B lymphocytes by Epstein-Barr virus (E BV) only a few viral genes are expressed, six of which encode the EBV nuclear antigens, EBNAs 1-6, The majority of EBNA mRNAs share common 5 '-ends containing a variable number of two alternating and repeated ex ons transcribed from the BamHI W major internal repeats of the viral D NA, These sequences can also exist as independent small RNA species in some EBV-infected cell types, We present evidence that transcripts fr om these W repeat regions can exert a trans-acting effect on protein s ynthesis, through their ability to activate the dsRNA-dependent protei n kinase PKR, UV cross-linking and filter binding assays have demonstr ated that the W transcripts bind specifically to PKR and can compete w ith another EBV-encoded small RNA, EBER-1, which was shown previously to bind this kinase, In the reticulocyte lysate system the W RNAs shut off protein synthesis through an ability to activate PKR, In contrast to EBER-1, the W RNAs are unable to block the dsRNA-dependent activat ion of PKR, Using a purified preparation of the protein kinase we have shown that the W transcripts directly activate PKR in vitro, The resu lts suggest that EBV has the ability both to activate and to inhibit P KR through the actions of different products of viral transcription.