THE OPEN READING FRAME (ORF) 50A GENE-PRODUCT REGULATES ORF-57 GENE-EXPRESSION IN HERPESVIRUS SAIMIRI

We have previously demonstrated that open reading frame (ORF) 50 and O RF 57 encode transcriptional regulating genes in herpesvirus saimiri. ORF 50, a homolog of Epstein-Barr virus R protein, is a sequence-speci fic transactivator, whereas ORF 57 acts posttranscriptionally. In this report, we demonstrate that the ORF 57 gene is regulated by the ORF 5 0a gene product. We show that the ORF 57 gene is expressed at basal le vels early in the virus replication cycle and that thereafter it is tr ansactivated by the ORF 50a gene product, due to an increase in RNA le vels. As it has been shown that the ORF 57 gene product downregulates ORF 50a due to the presence of its intron, these combined observations identify a feedback mechanism modulating gene expression in herpesvir us saimiri, whereby ORF 50a transcription is downregulated by the ORF 57 gene product, a gene which it specifically transactivates. Furtherm ore,,ve propose that the intron-containing ORF 57 gene downregulates i tself by the same mechanism as that for ORF 50a, as both genes are dow nregulated at similar times during the replication cycle.