Widespread Protection of RNA Cleavage Sites by a Riboswitch Aptamer that Folds as a Compact Obstacle to Scanning by RNase E.
Mol Cell 2020;
81:127-138.e4. [PMID:
33212019 DOI:
10.1016/j.molcel.2020.10.025]
[Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 10/14/2020] [Accepted: 10/15/2020] [Indexed: 12/26/2022]
Abstract
Riboswitches are thought generally to function by modulating transcription elongation or translation initiation. In rare instances, ligand binding to a riboswitch has been found to alter the rate of RNA degradation by directly stimulating or inhibiting nearby cleavage. Here, we show that guanidine-induced pseudoknot formation by the aptamer domain of a guanidine III riboswitch from Legionella pneumophila has a different effect, stabilizing mRNA by protecting distal cleavage sites en masse from ribonuclease attack. It does so by creating a coaxially base-paired obstacle that impedes scanning from a monophosphorylated 5' end to those sites by the regulatory endonuclease RNase E. Ligand binding by other riboswitch aptamers peripheral to the path traveled by RNase E does not inhibit distal cleavage. These findings reveal that a riboswitch aptamer can function independently of any overlapping expression platform to regulate gene expression by acting directly to prolong mRNA longevity in response to ligand binding.
Collapse