Characterization of open reading frame 50 response elements in Kaposi's sarcoma-associated herpesvirus promoters

Abstract

Kaposi’s sarcoma-associated herpesvirus (KSHV) belongs to a human gammaherpesvirus that has a latent phase in host cells. ORF50 protein is the most important protein in reactivation to lytic phase and it is known as a strong transcriptional activator. Transactivation of promoters by ORF50 is done via response elements, so we tried to find ORF50 response elements in ORF50, K8, and ORF57 promoters with transient transfection assays of deletion mutants. We found smaller regions for activation by ORF50 in three promoters. The patterns of each response element are quite different and there is no conservative sequence, so ORF50 protein response elements are heterogeneous. AP-1 protein is participated in ORF57 promoter activation by ORF50, this result can be acquired by competitive electrophoretic mobility shift assay. ORF57 protein is a homolog of ICP27, a pleiotropic protein. We supposed that CBP is mediated because of the fact that ORF57 repress CREB mediated transcriptional pathway and p53 mediated transcriptional activation, in virto binding assay showed direct binding of CBP2 fragment (C/H3 domain) and C-terminus of ORF57. We can conclude ORF57 protein has strong repressor activity and CBP is related to this ORF57 activity