Human hHpr1/p84/Thoc1 regulates transcriptional elongation and physically links RNA polymerase II and RNA processing factors.

Cotranscriptional loading of RNA processing factors onto nascent RNA facilitates efficient gene expression. Mechanisms responsible for coupling transcription and RNA processing are not well defined, but the Saccharomyces cerevisiae TREX complex provides an example. TREX is composed of the subcomplex THO that associates with RNA polymerase II and is required for normal transcriptional elongation. THO associates with proteins involved in RNA splicing and export to form the larger TREX complex. Hence, assembly of TREX physically couples transcriptional elongation with RNA processing factors. Whether metazoan species with long, intron-containing genes utilize a similar mechanism has not been established. Here we show that human hHpr1/p84/Thoc1 associates with elongating RNA polymerase II and the RNA splicing and export factor UAP56 in intact cells. Depletion of hHpr1/p84/Thoc1 causes transcriptional elongation defects and associated cellular phenotypes similar to those observed in THO-deficient yeast. We conclude that hHpr1/p84/Thoc1 regulates transcriptional elongation and may participate in a protein complex functionally analogous to yeast TREX, physically linking elongating RNA polymerase II with RNA processing factors.