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.