RNA-Degrading Exosome Complexes: Molecular Mechanisms and Structural Insights

The RNA exosome is a conserved multiprotein complex essential for 3'-to-5' RNA degradation in eukaryotic cells. In the cytoplasm, the exosome participates in messenger RNA surveillance and decay, while in the nucleus and nucleolus it performs a broader range of functions, from fully degrading cryptic RNAs generated by faulty or pervasive transcription to precisely trimming structured RNAs. An extended network of obligate cofactors and transient RNA helicase complexes has evolved to handle the large variety of substrates in each subcellular compartment. This network organizes in layers around the exosome core and regulates the irreversible 3'-to-5' degradative action in synergy with the features of the substrates. In this review, we discuss findings derived from genetic, cellular, biochemical, and structural analyses of nuclear and cytoplasmic exosome complexes, and integrate them into molecular movies that illustrate the mechanistic principles of this versatile and dynamic machine in RNA processing and RNA decay.