
<ArticleTitle>DNA binding by Kaposi's sarcoma-associated herpesvirus lytic switch protein is necessary for transcriptional activation of two viral delayed early promoters.</ArticleTitle>
<AbstractText>Kaposi's sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus-8) establishes latent and lytic infections in both lymphoid and endothelial cells and has been associated with diseases of both cell types. The <prot>KSHV open reading frame 50</prot> (<prot>ORF50</prot>) protein is a transcriptional activator that plays a central role in the reactivation of lytic viral replication from latency. Here we identify and characterize a DNA binding site for the <prot>ORF50</prot> protein that is shared by the promoters of two delayed early genes (<prot>ORF57</prot> and <prot>K-bZIP</prot>). Transfer of this element to heterologous promoters confers on them high-level responsiveness to <prot>ORF50</prot>, indicating that the element is both necessary and sufficient for activation. The element consists of a conserved 12-bp palindromic sequence and less conserved sequences immediately 3' to it. Mutational analysis reveals that sequences within the palindrome are critical for binding and activation by <prot>ORF50</prot>, but the presence of a palindrome itself is not absolutely required. The 3' flanking sequences also play a critical role in DNA binding and transactivation. The strong concordance of DNA binding in vitro with transcriptional activation in vivo strongly implies that sequence-specific DNA binding is necessary for <prot>ORF50</prot>-mediated activation through this element. Expression of truncated versions of the <prot>ORF50</prot> protein reveals that DNA binding is mediated by the amino-terminal 272 amino acids of the polypeptide.</AbstractText>
