The mediator couples transcription and splicing

Abstract

Transcription is coupled with pre-mRNA splicing in metazoans. In the current issue of Molecular Cell, Huang et al. (2012) show that Med23 interacts with the RNA binding protein hnRNP L to regulate alternative splicing, thus expanding Mediator's function beyond transcriptional control.

Figure 1

Initiating the coupling between transcription and RNA processing at gene promoter. hnRNP L is initially recruited to gene promoter via direct protein-protein interaction with Med23, a tail component of the large Mediator complex. This recruitment appears to also enhance Pol II binding at gene promoter. The recruited hnRNP L affects downstream splicing events by binding to CA-rich motifs in pre-mRNA, although the mechanism for the RNA binding protein to switch from Mediator to elongating Pol II and then to nascent RNA remains to be defined. This work highlights a new role of Mediator in coupling between transcription and pre-mRNA processing. Specific RNA binding proteins recruited to Mediator may also play critical roles in promoting enhancer-promoter communications via intergenic non-coding RNAs.