Lytic switch protein (ORF50) response element in the Kaposi’s sarcoma-associated herpesvirus K8 promoter is located within but does not require a palindromic structure

Kaposi’s sarcoma-associated virus (KSHV) ORF50 protein induces lytic replication and activates the K8 promoter. We show that ORF50-induced and tetradecanoyl phorbol acetate (TPA) induced K8 transcripts initiated from the same start site. A newly identified palindrome (PAL2), containing a 12-bp response region required for ORF50-induced activation in lymphoid cells, was identified in the K8 promoter. Specific DNA binding of bacterially expressed ORF50 was not seen with the K8 promoter despite specific binding to the PAN promoter. The new palindrome shared homology with a previously described ORF50 response element (50RE K8 and 50RE 57). We demonstrate that the new 50RE K8 (50RE K8-PAL2) is not the palindrome per se. Instead, the response element is buried within the right arm of the palindrome. We propose that the complexity of the K8 response elements reflects the complexity of mechanisms used by ORF50 during viral reactivation.