REPRESSION OF GENE-EXPRESSION BY AN EXOGENOUS SEQUENCE ELEMENT ACTINGIN CONCERT WITH A HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN-LIKE PROTEIN, NRD1, AND THE PUTATIVE HELICASE SEN1

We have fortuitously identified a nucleotide sequence that decreases e xpression of a reporter gene in the yeast Saccharomyces cerevisiae 20- fold when inserted into an intron, The primary effect of the insertion is a decrease in pre-mRNA abundance accompanied by the appearance of 3'-truncated transcripts, consistent with premature transcriptional te rmination and/or pre-mRNA degradation, Point mutations in the cis elem ent relieve the negative effect, demonstrating its sequence specificit y, A novel yeast protein, named Nrd1, and a previously identified puta tive helicase, Sen1, help mediate the negative effect of the cis eleme nt. Sen1 is an essential nuclear protein that has been implicated in a variety of nuclear functions, Nrd1 has hallmarks of a heterogeneous n uclear ribonucleoprotein, including an RNA recognition motif, a region rich in RE and RS dipeptides, and a proline- and glutamine-rich domai n, An N-terminal domain of Nrd1 may facilitate direct interaction with RNA polymerase II. Disruption of the NRD1 gene is lethal, yet C-termi nal truncations that delete the RNA recognition motif and abrogate the negative effect of the cia element nevertheless support cell growth, Thus, expression of a gene containing the cis element could be regulat ed through modulation of the activity of Nrd1. The recent identificati on of Nrd1-related proteins in mammalian cells suggests that this pote ntial regulatory pathway is widespread among eukaryotes.