Alternative splicing determines the carboxy terminus of the Epstein-Barr virus nuclear antigen 5 species expressed in the Burkitt's lymphoma cell

possesses a genomic deletion, relative to the B95-8 EBV prototype, that removes the entire Epstein-Barr virus nuclear antigen 2 (EBNA2) open reading frame (ORF) and the sequences ncoding the carboxy terminus of EBNA5. Immunoblot analysis carried out in this study indicates that two species of EBNA5 (31 K and 37K) are expressed in Daudi cells. Nucleotide sequence analysis of Daudi cDNA clones has con-firmed that, as a consequence of the genomic deletion, exons usually appearing further downstream in EBNA messages (exons U or HF) are spliced directly onto the truncated EBNA50RF. Furthermore, the use of alternative splicing suggests that the two EBNA5 species expressed in Daudi cells possess different carboxy termini. Infection of human B lymphocytes with Epstein-Barr virus (EBV) predominantly results in a latent infection, with little production of virions, and a concomitant immortalization of the infected cells. There are at least nine virus-encoded proteins expressed uring latent infection, and the genes encoding six of these, Epstein-Barr virus nuclear antigen 1 to 6 (EBNAs 1 to 6) are transcribed from a complex transcriptional unit span-ning the left-hand 100 kbp of the viral genome, as conventionally depicted. Transcription in most B cells is driven by either of two promoters, one in the BamHI C fragment (Cp) and the other in the BamHI W fragment (Wp). Transcripts initiating at Wp and Cp contain one and two unique xons at their 5 ' ends, respectively. These are spliced to a variable number of repeated exons (W1 and W2) encoded within the BamHI W repeat. The W2 exons splice either to another Wl exon, or to two or three exons encoded within the adjacent BamHI Y fragment (Y1, Y2 and Y3). The Y2 or Y3 exon is in turn spliced to, or contiguous with, unique 3 ' sequences which include those encoding EBNAs 1, 2, 3, 4 and 6 (reviewed i