CST (BART BARF0) family viral RNAs are expressed in several types of Epstei
n-Barr virus (EBV) infection, including EBV-associated cancers. Many differ
ent spliced forms of these RNAs have been described; here we have clarified
the structures of some of the more abundant splicing patterns. We report t
he first cDNAs representing a full-length CST mRNA from a clone library and
further characterize the transcription start. The relative abundance of sp
licing patterns and genomic analysis of the open reading frames (ORFs) sugg
est that, in addition to the much studied BARF0 ORF, there may be important
products made from some of the upstream ORFs in the CST RNAs. Potential bi
ological functions are identified for two of these. The product of the RPMS
1 ORF is shown to be a nuclear protein that can bind to the CBF1 component
of Notch signal transduction. RPMS1 can inhibit the transcription activatio
n induced through CBF1 by NotchIC or EBNA-2. The protein product of another
CST ORF, A73, is shown to be a cytoplasmic protein which can interact with
the cell RACK1 protein. Since RACK1 modulates signaling from protein kinas
e C and Src tyrosine kinases, the results suggest a possible role for CST p
roducts in growth control, perhaps consistent with the abundant transcripti
on of CST RNAs in cancers such as nasopharyngeal carcinoma.