Biology subjects

Qureshi, N. S.

Publications and source records attributed to Qureshi, N. S..

3 recordsLinked to original sources

bioRxiv2026

A bacterial nucleolus for cold adaptation

Compartmentalisation enables cells to spatially organise essential biochemical processes. This is exemplified by the eukaryotic nucleolus, which concentrates the machinery for ribosome biogenesis. Bacteria are generally thought to lack an equivalent compartment. Here we discover a nucleolus-like condensate in Escherichia coli that emerges at rDNA loci during cold adaptation to spatially organise and promote ribosome biogenesis. Low temperatures, which stabilise RNA secondary structures, induce accumulation of the RNA-remodelling enzyme CsdA. This raises the cellular CsdA concentration above its condensation threshold, driving condensate formation at rDNA loci when rRNA transcription is active. CsdA compartments enrich the rRNA transcription machinery and ribosome-biogenesis factors, spatially linking rRNA synthesis to downstream processing and assembly. Disrupting CsdA condensation impairs ribosome maturation and reduces bacterial adaptation to cold temperature, demonstrating functional importance of condensate formation. Comparative genomics suggests that analogous condensate-forming RNA remodelling enzymes have evolved repeatedly across diverse bacterial lineages. Our findings establish biomolecular condensates as a unifying organisational principle of ribosome biogenesis across the tree of life and suggest that adaptive compartmentalisation can emerge when environmental conditions challenge the efficiency of essential biochemical processes.

cell biology↗

bioRxiv2026

Functional coupling between ribosomal RNA transcription and processing guided by stable transcription factor binding

Coordinating ribosomal RNA (rRNA) transcription, folding and processing is essential for bacterial ribosome assembly. Yet, the molecular mechanisms underlying this coordination remain poorly understood. Particularly, whether the rRNA transcription antitermination complex (rrnTAC: NusA, NusG, NusB, NusE, S4, SuhB) orchestrates this coordination remains unclear. Here, we develop a suite of multi-color single-molecule fluorescence microscopy assays to simultaneously visualize, in real-time, rrnTAC assembly dynamics and their effect on transcription and co-transcriptional processing by RNase III. We find that transient ([~]1 s) interactions of general transcription factors NusA and NusG with RNAP, and of NusB/E with the rRNA-specific boxBAC element, are stabilized to minutes-long residence by final SuhB recruitment. Stable rrnTAC assembly is required to reduce RNAP pausing and to boost co-transcriptional rRNA processing. Collectively, our results reveal how transcription factor binding dynamics relate to function: transient for messenger RNA transcription and stable for rRNA transcription and processing.

biophysics↗

bioRxiv2023

Tracking transcription-translation coupling in real-time

A central question in biology is how macromolecular machines function cooperatively. In bacteria, transcription and translation occur in the same cellular compartment and can be physically and functionally coupled. While several recently published high-resolution structures of the ribosome-RNA polymerase (RNAP) complex provided first mechanistic insight into the coupling process, we do not know how these structural snapshots are placed along a dynamic reaction trajectory. Here, we reconstitute a complete active transcription-translation system and develop multi-color single-molecule fluorescence microscopy experiments to directly and simultaneously track transcription elongation, translation elongation and the physical and functional coupling between the ribosome and the RNAP in real-time. Our data show that the ribosome slows down while colliding with the RNAP and that coupling following a collision becomes less efficient. Unexpectedly, physical coupling can occur with hundreds of nucleotides of intervening mRNA between both machineries by mRNA looping, and increases in efficiency in presence of NusG. We detect active transcription elongation during mRNA looping and show that NusA-paused RNAPs can be activated by the ribosome by long-range physical coupling. We provide an alternative explanation on how the ribosome can rescue RNAP from frequent pausing without requiring collisions by a closely trailing ribosome. Our data mechanistically highlight an example of how macromolecular machines central to gene expression physically and functionally cooperate.

biophysics↗