Characterization of Kaposi's sarcoma-associated herpesvirus/human herpesvirus-8 ORF57 promoter

Kaposi's sarcoma-associated herpesvirus (KSHV) is a recently discovered hum an gamma herpesvirus (HHV-8) that plays an important role in Kaposi's sarco ma development. Here, we further characterize the regulation of the early H HV-8 gene, open reading frame 57 (ORF57). ORF57 is a spliced gene consistin g of two exons with a 108-bp intron near the 5' end. The ORF57 mRNA can pot entially be initiated at two different start sites, and its expression can be significantly stimulated by ORF50, an HHV-8 immediate early gene. The ta rget site for ORF50 transactivation was mapped to a 40-bp fragment compassi ng nt 81904 to 81943 in the ORF57 promoter. Our study on the regulation of ORF57 expression by ORF50 provides the basis for further studies on the reg ulation of HHV-8 lytic gene expression.