title: Structures of 5'-3' Exoribonucleases.
abstract: 5'-3' Exoribonucleases (XRNs) have important functions in RNA processing, RNA turnover and decay, RNA interference, RNA polymerase transcription, and other cellular processes. Their sequences share two highly conserved regions, CR1 and CR2. The cytoplasmic Xrn1 and the nuclear Xrn2/Rat1 are found in yeast and animals, and XRNs are found in most other eukaryotes. Crystal structures of Xrn1 and Rat1 have been reported recently, offering the first detailed information on these enzymes. The two conserved regions of XRNs form a single, large domain. CR1 has structural homology with the FEN superfamily of nucleases, while CR2 restricts access to the active site, ensuring that XRNs are exclusive exoribonucleases. The structure of Rai1, the protein partner of Rat1, revealed the presence of an active site, and further studies demonstrated that this activity is a novel mechanism for mRNA 5'-end capping quality surveillance.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY, USA.
authors.forename: Jeong Ho
authors.initials: JH
authors.lastname: Chang
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY, USA; Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, PR China.
authors.forename: Song
authors.initials: S
authors.lastname: Xiang
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY, USA. Electronic address: ltong@columbia.edu.
authors.forename: Liang
authors.initials: L
authors.lastname: Tong
keywords: Dom3Z; Nonsense-mediated decay; Rai1; Rat1; Transcription termination; Xrn1; Xrn2; mRNA capping; mRNA turnover