A. Whitehouse et al., THE IMMEDIATE-EARLY GENE-PRODUCT ENCODED BY OPEN READING FRAME-57 OF HERPESVIRUS SAIMIRI MODULATES GENE-EXPRESSION AT A POSTTRANSCRIPTIONALLEVEL, Journal of virology, 72(1), 1998, pp. 857-861
The herpesvirus saimiri (HVS) immediate-early gene product encoded by
open reading frame (ORF) 57 shares limited amino acid homology with HS
V-1 ICP27 and Epstein-Barr virus BMLF1, both regulatory proteins. The
ORF 57 gene has been proposed to be spliced based on the genome sequen
ce, and here we confirm the intron-exon structure of the gene. We also
demonstrate that a cDNA construct of the ORF 57 gene product represse
s the transactivating capability of the ORF 50a gene product (which is
produced from a spliced transcript), but activates that of ORF 50b (a
n unspliced transcript). Further analyses with cotransfection experime
nts show that ORF 57 can either activate or repress expression from a
range of both early and late RVS promoters, depending on the target ge
ne. These results indicate that repression of gene expression mediated
by the ORF 57 gene product is dependent on the presence of an intron
within the target gene encoding region. Furthermore, Northern blot ana
lysis demonstrates that the levels of mRNA transcribed from genes not
containing an intron are not significantly affected in the presence of
the ORF 57 gene product. This suggests that it regulates gene express
ion through a posttranscriptional mechanism.