The Nrd1–Nab3–Sen1 transcription termination complex from a structural perspective

A substantial part of living cells activity involves transcription regulation. The RNA polymerases responsible for this job need to know ‘where/when' to start and stop in the genome, answers that may change throughout life and upon external stimuli. In Saccharomyces cerevisiae, RNA Pol II transcription termination can follow two different routes: the poly(A)-dependent one used for most of the mRNAs and the Nrd1/Nab3/Sen1 (NNS) pathway for non-coding RNAs (ncRNA). The NNS targets include snoRNAs and cryptic unstable transcripts (CUTs) generated by pervasive transcription. This review recapitulates the state of the art in structural biology and biophysics of the Nrd1, Nab3 and Sen1 components of the NNS complex, with special attention to their domain structures and interactions with peptide and RNA motifs, and their heterodimerization. This structural information is put into the context of the NNS termination mechanism together with possible prospects for evolution in the field.