TRAMP Stimulation of Exosome.

In order to control and/or enhance the specificity and activity of nuclear surveillance and degradation, exosomes cooperate with the polyadenylation complex called TRAMP. Two forms of TRAMP operate in budding yeast, TRAMP4 and TRAMP5. They oligoadenylate defective or precursor forms of RNAs and promote trimming or complete degradation by exosomes. TRAMPs target a wide variety of nuclear transcripts. The known substrates include the noncoding RNAs originating from pervasive transcription from diverse parts of the yeast genome. Although TRAMP and exosomes can be triggered to a subset of their targets via the RNA-binding complex Nrd1, it is still not completely understood how TRAMP recognizes other aberrant RNAs. The existence of TRAMP-like complexes in other organisms indicates the importance of nuclear surveillance for general cell biology. In this chapter, we review the current understanding of TRAMP function and substrate repertoire. We discuss the advances in TRAMP biochemistry with respect to its catalytic activities and RNA recognition. Finally, we speculate about the possible mechanisms by which TRAMP activates exosomes.