A nascent riboswitch helix orchestrates robust transcriptional regulation through signal integration.

Widespread manganese-sensing transcriptional riboswitches effect the dependable gene regulation needed for bacterial manganese homeostasis in changing environments. Riboswitches - like most structured RNAs - are believed to fold co-transcriptionally, subject to both ligand binding and transcription events; yet how these processes are orchestrated for robust regulation is poorly understood. Through a combination of single-molecule and bulk approaches, we discover how a single Mn ion and the transcribing RNA polymerase (RNAP), paused immediately downstream by a DNA template sequence, are coordinated by the bridging switch helix P1.

A nascent riboswitch helix orchestrates robust transcriptional regulation through signal integration.

Widespread manganese-sensing transcriptional riboswitches effect the dependable gene regulation needed for bacterial manganese homeostasis in changing environments. Riboswitches - like most structured RNAs - are believed to fold co-transcriptionally, subject to both ligand binding and transcription events; yet how these processes are orchestrated for robust regulation is poorly understood. Through a combination of single molecule and bulk approaches, we discovered how a single Mn ion and the transcribing RNA polymerase (RNAP), paused immediately downstream by a DNA template sequence, are coordinated by the bridging switch helix P1.

Looking at Biomolecular Interactions through the Lens of Correlated Fluorescence Microscopy and Optical Tweezers.

Understanding complex biological events at the molecular level paves the path to determine mechanistic processes across the timescale necessary for breakthrough discoveries. While various conventional biophysical methods provide some information for understanding biological systems, they often lack a complete picture of the molecular-level details of such dynamic processes. Studies at the single-molecule level have emerged to provide crucial missing links to understanding complex and dynamic pathways in biological systems, which are often superseded by bulk biophysical and biochemical studies.

Precise tuning of bacterial translation initiation by non-equilibrium 5'-UTR unfolding observed in single mRNAs.

Noncoding, structured 5'-untranslated regions (5'-UTRs) of bacterial messenger RNAs (mRNAs) can control translation efficiency by forming structures that either recruit or repel the ribosome. Here we exploit a 5'-UTR embedded preQ1-sensing, pseudoknotted translational riboswitch to probe how binding of a small ligand controls recruitment of the bacterial ribosome to the partially overlapping Shine-Dalgarno (SD) sequence. Combining single-molecule fluorescence microscopy with mutational analyses, we find that the stability of 30S ribosomal subunit binding is inversely correlated with the free energy needed to unfold the 5'-UTR during mRNA accommodation into the mRNA binding cleft.

A translational riboswitch coordinates nascent transcription-translation coupling.

Bacterial messenger RNA (mRNA) synthesis by RNA polymerase (RNAP) and first-round translation by the ribosome are often coupled to regulate gene expression, yet how coupling is established and maintained is ill understood. Here, we develop biochemical and single-molecule fluorescence approaches to probe the dynamics of RNAP-ribosome interactions on an mRNA with a translational preQ-sensing riboswitch in its 5' untranslated region. Binding of preQ leads to the occlusion of the ribosome binding site (RBS), inhibiting translation initiation.

Transcriptional Riboswitches Integrate Timescales for Bacterial Gene Expression Control.

Transcriptional riboswitches involve RNA aptamers that are typically found in the 5' untranslated regions (UTRs) of bacterial mRNAs and form alternative secondary structures upon binding to cognate ligands. Alteration of the riboswitch's secondary structure results in perturbations of an adjacent expression platform that controls transcription elongation and termination, thus turning downstream gene expression "on" or "off." Riboswitch ligands are typically small metabolites, divalent cations, anions, signaling molecules, or other RNAs, and can be part of larger signaling cascades.

Local-to-global signal transduction at the core of a Mn sensing riboswitch.

The widespread Mn-sensing yybP-ykoY riboswitch controls the expression of bacterial Mn homeostasis genes. Here, we first determine the crystal structure of the ligand-bound yybP-ykoY riboswitch aptamer from Xanthomonas oryzae at 2.96 Å resolution, revealing two conformations with docked four-way junction (4WJ) and incompletely coordinated metal ions.

Investigating the molecular and aggregated states of a drug molecule rutaecarpine using spectroscopy, microscopy, crystallography and computational studies.

The photophysical properties of a potential drug molecule rutaecarpine have been investigated in molecular as well as aggregated states. All systems have been characterized by various spectroscopic, microscopic and dynamic light scattering (DLS) techniques. The investigation has been carried out by keeping the fact in mind that hydrophobic organic molecules have a strong tendency to form aggregates in aqueous solution.