New clues to understand the role of THO and other functionally related factors in mRNP biogenesis.

Coupling of transcription with mRNA processing and export has been shown to be relevant to efficient gene expression. A number of studies have determined that THO/TREX, a nuclear protein complex conserved from yeast to humans, plays an important role in mRNP biogenesis connecting transcription elongation, mRNA export and preventing genetic instability. Recent data indicates that THO could be relevant to different mRNA processing steps, including the 3'-end formation, transcript release and export. Novel connections of THO to proteins related to the splicing machinery, provide new views about possible functions of THO in mRNP biogenesis. In this review, we summarize the previous and new results concerning the impact of THO in transcription and its biological implications, with a special emphasis on the relationship with THSC/TREX-2 and other functionally related factors involved in mRNA biogenesis and export. The emerging picture presents THO as a dynamic complex interacting with the nascent RNA and with different factors connecting nuclear functions necessary for mRNP biogenesis with genome integrity, cellular homeostasis and development. This article is part of a Special Issue entitled: Nuclear Transport and RNA Processing.