No abstract

During the initial infection of B lymphocytes by Epstein-Barr virus (EBV) 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 exons transcribed from the BamHI W major internal repeats of the viral DNA. These sequences can also exist as independent small RNA species in some EBV-infected cell types. We present evidence that transcripts from these W repeat regions can exert a trans-acting effect on protein synthesis, through their ability to activate the dsRNA-dependent protein kinase PKR. UV cross-linking and filter binding assays have demonstrated that the W transcripts bind specifically to PKR and can compete with 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 activation of PKR. Using a purified preparation of the protein kinase we have shown that the W transcripts directly activate PKR in vitro. The results suggest that EBV has the ability both to activate and to inhibit PKR through the actions of different products of viral transcription.

No abstract