Abstract

The Kaposi's sarcoma-associated herpesvirus produces a 1077 nucleotide noncoding, polyadenylated, exclusively nuclear RNA called PAN that is highly expressed in lytically infected cells. We report that PAN contains a novel post-transcriptional element essential for its abundant accumulation. The element, PAN–ENE (PAN RNA expression and nuclear retention element), increases the efficiency of 3'-end formation in vivo and is sufficient to enhance RNA abundance from an otherwise inefficiently expressed intronless -globin construct. The PAN–ENE does not concomitantly increase the production of encoded protein. Rather, it retains the unspliced -globin mRNA in the nucleus. Tethering of export factors can override the nuclear retention of the PAN–ENE, supporting a mechanism whereby the PAN–ENE blocks assembly of an export-competent mRNP. The activities of the PAN–ENE are specific to intronless constructs, since inserting the PAN–ENE into a spliced -globin construct has no effect on mRNA abundance and does not affect localization. This is the first characterization of a cis-acting element that increases RNA abundance of intronless transcripts but inhibits assembly of an export-competent mRNP.