Transcription termination and the control of the transcriptome: why, where and how to stop.

Transcription termination occurs when the polymerase is released after a transcription event, thus delimitating transcription units; however, the functional importance of termination extends beyond the mere definition of gene borders. By determining the cellular fate of the generated transcripts, transcription termination pathways shape the transcriptome. Recent reports have underscored the crucial role of these pathways in limiting the extent of pervasive transcription, which has attracted interest in post-initiation events in gene expression control. Transcription termination pathways involved in the production of non-coding RNAs - such as the Nrd1-Nab3-Sen1 (NNS) pathway in yeast and the cap-binding complex (CBC)-ARS2 pathway in humans - are key determinants of transcription quality control. Understanding the mechanisms leading to the timely and efficient dismantling of elongation complexes remains a major unmet challenge, but new insights into the molecular basis of termination at mRNA-coding and non-coding RNA gene targets have been gained in eukaryotes.