Molecular genetic analysis of Epstein-Barr virus Cp promoter function

The Cp promoter of Epstein-Barr virus (EBV) directs most transcription of the EBNA genes in lymphoblastoid cell lines. The functions of two control regions in the Cp promoter have been studied by construction of recombinant EBV strains containing specific mutations in these elements. Mutation of the RBP-Jk (CBF1) binding site reduced but did not completely abolish EBNA-2-dependent Cp activity in transient transfection assays. The same mutation in recombinant virus gave only a modest average reduction in Cp function, ranging from full activity to almost no activity in different isolates. Separate deletion of a 262-bp region containing glucocorticoid response elements had little effect in a transient assay but caused a fivefold increase in the steady-state level of Cp RNA in recombinant virus. The results indicate that other elements in addition to the intensively studied RBP-Jk site are important in determining Cp activity in the whole virus. Clonal EBV-infected cell lines expressed RNA from both the Cp and Wp promoters, but the level of Wp RNA did not simply compensate for changes in the level of Cp RNA. The levels of EBNA proteins varied much less than the levels of Cp and Wp RNA, suggesting other types of control in addition to initiation of transcription. A survey of RNAs derived from the internal repeat region of the virus indicated that gene expression from this region of EBV in lymphoblastoid cell lines is accounted for by the known transcripts.