5 years ago

Capture and Release of tRNA by the T-Loop Receptor in the Function of the T-Box Riboswitch

Capture and Release of tRNA by the T-Loop Receptor in the Function of the T-Box Riboswitch
Edward P. Nikonowicz, Malgorzata Michnicka, Xianyang Fang, Yikan Zhang, Yun-Xing Wang
In Gram-positive bacteria, the tRNA-dependent T-box riboswitch system regulates expression of amino acid biosynthetic and aminoacyl-tRNA synthetase genes through a transcription attenuation mechanism. Binding of uncharged tRNA “closes” the switch, allowing transcription read-through. Structural studies of the 100-nucleotide stem I domain reveal tRNA utilizes base pairing and stacking interactions to bind the stem, but little is known structurally about the 180-nucleotide riboswitch core (stem I, stem III, and antiterminator stem) in complex with tRNA or the mechanism of coupling of the intermolecular binding domains crucial to T-box function. Here we utilize solution structural and biophysical methods to characterize the interplay of the different riboswitch–tRNA contact points using Bacillus subtilis and Oceanobacillus iheyensis glycyl T-box and T-box:tRNA constructs. The data reveal that tRNA:riboswitch core binding at equilibrium involves only Specifier–anticodon and antiterminator–acceptor stem pairing. The elbow:platform stacking interaction observed in studies of the T-box stem I domain is released after pairing between the acceptor stem and the bulge in the antiterminator helix. The results are consistent with the model of T-box riboswitch:tRNA function in which tRNA is captured by stem I of the nascent mRNA followed by stabilization of the antiterminator helix and the paused transcription complex.

Publisher URL: http://dx.doi.org/10.1021/acs.biochem.7b00284

DOI: 10.1021/acs.biochem.7b00284

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