THE LYTIC ORIGIN OF HERPESVIRUS PAPIO IS HIGHLY HOMOLOGOUS TO EPSTEIN-BARR-VIRUS ORI-LYT - EVOLUTIONARY CONSERVATION OF TRANSCRIPTIONAL ACTIVATION AND REPLICATION SIGNALS

Herpesvirus papio (HVP) is a B-lymphotropic baboon virus with an estim ated 40% homology to Epstein-Barr virus (EBV). We have cloned and sequ enced ori-Lyt of herpesvirus papio and found a striking degree of nucl eotide homology (89%) with ori-Lyt of EBV. Transcriptional elements fo rm an integral part of EBV ori-Lyt. The promoter and enhancer domains of EBV ori-Lyt are conserved in herpesvirus papio. The EBV ori-Lyt pro moter contains four binding sites for the EBV lytic cycle transactivat or Zta, and the enhancer includes one Zta and two Rta response element s. All five of the Zta response elements and one of the Rta motifs are conserved in HVP ori-Lyt, and the HVP DS-L leftward promoter and the enhancer were activated in transient transfection assays by the EBV Zt a and Rta transactivators. The EBV ori-Lyt enhancer contains a palindr omic sequence, GGTCAGCTGACC, centered on a PvuII restriction site. Thi s sequence, with a single base change, is also present in the HVP ori- Lyt enhancer. DNase I footprinting demonstrated that the PvuII sequenc e was bound by a protein present in a Raji nuclear extract. Mobility s hift and competition assays using oligonucleotide probes identified th is sequence as a binding site for the cellular transcription factor ML TF. Mutagenesis of the binding site indicated that MLTF contributes si gnificantly to the constitutive activity of the ori-Lyt enhancer. The high degree of conservation of cis-acting signal sequences in HVP ori- Lyt was further emphasized by the finding that an HVP ori-Lyt-containi ng plasmid was replicated in Vero cells by a set of cotransfected EBV replication genes. The central domain of EBV ori-Lyt contains two rela ted AT-rich palindromes, one of which is partially duplicated in the H VP sequence. The AT-rich palindromes are functionally important cis-ac ting motifs. Deletion of these palindromes severely diminished replica tion of an ori-Lyt target plasmid.