期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：50
页码：14306-14311
DOI：10.1073/pnas.1607512113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceRNAs are intimately involved in numerous cellular functions such as gene expression. Typically, RNAs adopt a 3D fold, and their sequences may be chemically altered to contain modified nucleotides such as pseudouridines. There are many RNA modification enzymes, but often their cellular functions remain unknown. In this proof-of-principle study, we show that the tRNA pseudouridine synthase TruB is a tRNA chaperone. In contrast to its modification activity, the ability of TruB to fold tRNA is critical for cellular fitness. It is likely that other modification enzymes and RNA-binding proteins act as RNA chaperones increasing the efficiency of RNA maturation. This connection of RNA modification with RNA folding may have arisen during the evolution from an RNA to a ribonucleoprotein world. Cellular RNAs are chemically modified by many RNA modification enzymes; however, often the functions of modifications remain unclear, such as for pseudouridine formation in the tRNA T{Psi}C arm by the bacterial tRNA pseudouridine synthase TruB. Here we test the hypothesis that RNA modification enzymes also act as RNA chaperones. Using TruB as a model, we demonstrate that TruB folds tRNA independent of its catalytic activity, thus increasing the fraction of tRNA that can be aminoacylated. By rapid kinetic stopped-flow analysis, we identified the molecular mechanism of TruBs RNA chaperone activity: TruB binds and unfolds both misfolded and folded tRNAs thereby providing misfolded tRNAs a second chance at folding. Previously, it has been shown that a catalytically inactive TruB variant has no phenotype when expressed in an Escherichia coli truB KO strain [Gutgsell N, et al. (2000) RNA 6(12):1870-1881]. However, here we uncover that E. coli strains expressing a TruB variant impaired in tRNA binding and in in vitro tRNA folding cannot compete with WT E. coli. Consequently, the tRNA chaperone activity of TruB is critical for bacterial fitness. In conclusion, we prove the tRNA chaperone activity of the pseudouridine synthase TruB, reveal its molecular mechanism, and demonstrate its importance for cellular fitness. We discuss the likelihood that other RNA modification enzymes are also RNA chaperones.
