The gene product encoded by ORF 57 of herpesvirus saimiri regulates the redistribution of the splicing factor SC-35

The herpesvirus saimiri (HVS) gene product encoded by ORF 57 shares limited C-terminal similarity with herpes simplex virus 1 ICP27, a protein that ha s been demonstrated to be involved in the inhibition of host-cell splicing and is responsible for the redistribution of components of the spliceosome. It has previously been shown that ORF 57 can either activate or repress vi ral gene expression by a post-transcriptional mechanism. Furthermore, repre ssion of gene expression by ORF 57 is dependent on the presence of an intro n within the target gene coding region. In this report, it is shown that HV S infection results in the redistribution of the SC-35 splicing factor in t he infected cell nucleus. Furthermore, the redistributed SC-35 colocalized with the ORF 57 protein product and expression of the protein alone was suf ficient to cause the redistribution of the spliceosome components. These re sults suggest that the mechanism by which ORF 57 downregulates expression o f intron-containing genes involves the redistribution of the spliceosome co mplex.