Gene expression during the latent and replicative states of the Epstein-Barr virus
This is an Open Access Thesis
Gene expression of the Epstein-Barr virus (EBV) was examined during the latent and lytic viral cycles. During latency the virus expresses two small RNAs (EBERs) and the EB nuclear antigen (EBNA). A gene encoding one peptide of the EBNA complex was mapped using S1 nuclease analysis. EBNA peptide is encoded by a 2028 base exon contained within the EBV Bam HI K fragment; the 3$\sp\prime$ end of this exon occurs 30 bp after the polyadenylation signal AATAAA and the 5$\sp\prime$ end occurs within a splice acceptor site. The latent state was disrupted experimentally by treatment with phorbol ester or superinfection with a defective HR-1 virus. Constitutive expression of the EBERs and of the EBNA message and peptide was shown to be unaffected by induction. However, many new viral messages were synthesized after induction. The Northern blotting technique was used to determine the size and genomic location of messenger RNAs expressed during the lytic cycle in a cellular clone of the HR-1 Burkitt Lymphoma line. At least 54 viral messages were identified, 28 of which were considered abundant. The structure of two lytic-cycle genes contained within Bam HI K was determined. In contrast to the EBNA message, these messenger RNAs of 1.3 kb and 2.1 kb are not expressed during latency, are abundantly induced with phorbol ester and are unspliced. Promoter regions of these two genes are similar to each other and to replicative promoters mapped in other regions of the EBV genome. An unusual feature of these replicative genes is that the smaller message begins within a long open reading frame of the larger message. Both messenger RNAs encode late antigens; the more abundant 1.3 kb message encodes a 22 kD peptide. The promoter of this late EBV gene was used to transcribe chloramphenicol acetyl transferase on cloned plasmids. Tentative experiments suggest that sequences within the untranslated leader have enhancer activity.