Transcription
Transcription is the primary control point for gene expression. It therefore determines cellular function and cell identity, and must be tightly regulated to achieve a high degree of specificity. Thus, it is not surprising that transcription is subject to regulation at each of its steps — initiation, elongation and termination. Many proteins, RNAs and features of chromatin are involved in these regulatory steps to ensure that, in each cell, the transcriptional machinery is recruited and activated at specific genes, progresses through chromatin at appropriate rates, and terminates in a controlled manner.
This specially commissioned Focus issue highlights the exquisite complexity of transcription regulation. Recent structural information on RNA polymerase II (Pol II) initiation complexes provides insight into the mechanisms by which Pol II binds specific promoters and initiates RNA synthesis. At the genome-wide level, we now have a better understanding of how the selective activation of enhancers drives cell-specific gene expression, how promoter-proximal pausing of Pol II and transcription elongation rates affect gene expression and co-transcriptional processes, and how transcription termination pathways contribute to shaping the transcriptome. Insights have also been gained into the mechanisms that enable transcription-associated histone exchange and chromatin remodelling and into the important functions of the Mediator complex in the regulation of enhancer–promoter gene looping, transcription initiation and elongation.
