The transcription–export link

Transcription is a congested business, with many different proteins crowding in to exert their influence. Now Katja Sträßer, Ed Hurt (University of Heidelberg, Germany), and colleagues have found that even nuclear export proteins get into the act, via an interaction with transcription elongation factors. The findings suggest that transcription, splicing and nuclear export are linked processes, and that there are many levels of regulation between these processes that remain to be discovered.Hurt found that yeast protein Sub2, which with Yra1 connects directly to mRNA exporters, binds a collection of proteins that make up the THO complex. This complex promotes transcription by acting on the elongation step.

The proposed connections were confirmed by synthetic lethal interactions, and with human homologues of the THO proteins. Hurt and colleagues named the combined complex the transcription–export or TREX complex, and found that proteins in the complex could be tracked by chromatin immunoprecipitation as they moved along a transcribed gene with RNA polymerase.

Mutants lacking a THO component had an mRNA export defect, but Hurt does not think that transcripts get posted directly from a gene into a nuclear pore complex. Transcription occurs throughout the nucleoplasm, and TREX factor binding at these sites may simply allow nuclear pores to capture mRNA–protein complexes after they diffuse away from these sites. ▪

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