Molecular biology: Mediating transcription and RNA export

Abstract

The finding that the Mediator protein complex contributes to messenger RNA export from the nucleus in yeast adds to a growing list of roles for the complex in regulating transcriptional processes.

Figure 1. Complex interactions in mRNA export

Following gene transcription, messenger RNA transcripts are poly-adenylated (adenine (A) bases are added to the 3’ end of the transcript) and disassociate from the transcribing enzyme RNA polymerase II (pol II).During and after transcription, factors involved in export of mRNA from the nucleus, such as the TREX- 2 protein complex, can associate with the mRNA. Schneider et al. report that mRNA export is regulated by interactions between TREX-2 and another protein complex, Mediator. In yeast, the Mediator–TREX-2 interaction seems to stabilize Mediator’s association with its Cdk8 kinase module — possibly through the TREX-2 subunit Sac3 and a subunit of Mediator called Med31. Mediator–TREX-2 interactions help ensure that genes undergoing transcription are close to the nuclear pore complex (NPC), thus facilitating mRNA export to the cytoplasm.