Structural insights into nuclear transcription by eukaryotic DNA-dependent RNA polymerases

Nuclear transcription of a wide variety of RNA species is conducted mainly by three RNA polymerases, which are large and dynamic protein complexes. Recent structural studies have provided important insights into the activities at different transcription stages and the commonalities and differences between these transcription machineries. The eukaryotic transcription apparatus synthesizes a staggering diversity of RNA molecules. The labour of nuclear gene transcription is, therefore, divided among multiple DNA-dependent RNA polymerases. RNA polymerase I (Pol I) transcribes ribosomal RNA, Pol II synthesizes messenger RNAs and various non-coding RNAs (including long non-coding RNAs, microRNAs and small nuclear RNAs) and Pol III produces transfer RNAs and other short RNA molecules. Pol I, Pol II and Pol III are large, multisubunit protein complexes that associate with a multitude of additional factors to synthesize transcripts that largely differ in size, structure and abundance. The three transcription machineries share common characteristics, but differ widely in various aspects, such as numbers of RNA polymerase subunits, regulatory elements and accessory factors, which allows them to specialize in transcribing their specific RNAs. Common to the three RNA polymerases is that the transcription process consists of three major steps: transcription initiation, transcript elongation and transcription termination. In this Review, we outline the common principles and differences between the Pol I, Pol II and Pol III transcription machineries and discuss key structural and functional insights obtained into the three stages of their transcription processes.

Automated summary

The transcription of RNA is mainly conducted by three RNA polymerases, which have similarities and differences in structure and function. Each RNA polymerase is responsible for synthesizing different types of RNA molecules, and the transcription process consists of three stages: initiation, elongation, and termination.