Abstract
SummaryPolynucleotide phosphorylase (PNPase) is an ancient exoribonuclease conserved in the course of evolution and is found in species as diverse as bacteria and humans. Paradoxically, Escherichia coli PNPase can act not only as an RNA degrading enzyme but also by an unknown mechanism as a chaperone for small regulatory RNAs (sRNAs), with pleiotropic consequences for gene regulation. We present structures of the ternary assembly formed by PNPase, the RNA chaperone Hfq, and sRNA and show that this complex boosts sRNA stability in vitro. Comparison of structures for PNPase in RNA carrier and degradation modes reveals how the RNA is rerouted away from the active site through interactions with Hfq and the KH and S1 domains. Together, these data explain how PNPase is repurposed to protect sRNAs from cellular ribonucleases such as RNase E and could aid RNA presentation to facilitate regulatory actions on target genes.
Highlights
In all domains of life, ribonucleases are key players in post-transcriptional regulation of gene expression
The path of RNA engaged by E. coli Polynucleotide phosphorylase (PNPase) in phosphorolytic mode Structures of E. coli apo PNPase have been limited to the catalytic core and parts of the KH domains (Nurmohamed et al, 2009)
While the catalytic core performs the phosphorolytic action, the KH and S1 domains participate in RNA substrate capture and autoregulation (Wong et al, 2013) and are powerful facilitators of PNPase activity
Summary
In all domains of life, ribonucleases are key players in post-transcriptional regulation of gene expression. These enzymes catalyze mRNA degradation and the maturation of rRNA and tRNA precursors, and they often have an impact on the stability of regulatory RNAs (Deutscher, 2015). PNPase can catalyze the polymerization of nucleotides, its main cellular function is the 3ʹ-to-5ʹ degradation of RNA (Grunberg-Manago et al, 1955). This reaction, phosphorolysis, requires inorganic phosphate and magnesium ions as cofactors and releases ribonucleoside diphosphates (rNDPs) as products (Nurmohamed et al, 2009)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
