conducting-multiple-imaging-modes-with-one-fluorescence-microscope

Conducting Multiple Imaging Modes with One Fluorescence Microscope

Fluorescence microscopy is a powerful tool to detect biological molecules in situ and monitor their dynamics and interactions in real-time. In addition to ...

University of Chicago

The bacterial small RNA (sRNA) SgrS has been a fruitful model for discovery of novel RNA-based regulatory mechanisms and new facets of bacterial physiology and metabolism. SgrS is one of only a few characterized dual-function sRNAs. SgrS can control gene expression posttranscriptionally via sRNA-mRNA base-pairing interactions. Its second function is coding for the small protein SgrT. Previous work demonstrated that both functions contribute to relief of growth inhibition caused by glucose-phosphate stress, a condition characterized by disrupted glycolytic flux and accumulation of sugar phosphates. The base-pairing activity of SgrS has been the subject of numerous studies, but the activity of SgrT is less well characterized. Here, we provide evidence that SgrT acts to specifically inhibit the transport activity of the major glucose permease PtsG. Superresolution microscopy demonstrated that SgrT localizes to the cell membrane in a PtsG-dependent manner. Mutational analysis determined that residues in the N-terminal domain of PtsG are important for conferring sensitivity to SgrT-mediated inhibition of transport activity. Growth assays support a model in which SgrT-mediated inhibition of PtsG transport activity reduces accumulation of nonmetabolizable sugar phosphates and promotes utilization of alternative carbon sources by modulating carbon catabolite repression. The results of this study expand our understanding of a basic and well-studied biological problem, namely, how cells coordinate carbohydrate transport and metabolism. Further, this work highlights the complex activities that can be carried out by sRNAs and small proteins in bacteria. Sequencing, annotation and investigation of hundreds of bacterial genomes have identified vast numbers of small RNAs and small proteins, the majority of which have no known function. In this study, we explore the function of a small protein that acts in tandem with a well-characterized small RNA during metabolic stress to help bacterial cells maintain balanced metabolism and continue growing. Our results indicate that this protein acts on the glucose transport system, inhibiting its activity under stress conditions in order to allow cells to utilize alternative carbon sources. This work sheds new light on a key biological problem: how cells coordinate carbohydrate transport and metabolism. The study also expands our understanding of the functional capacities of small proteins.

The Small Protein SgrT Controls Transport Activity of the Glucose-Specific Phosphotransferase System.

We report a robust nonparametric descriptor, J'(r), for quantifying the density of clustering molecules in single-molecule localization microscopy. J'(r), based on nearest neighbor distribution functions, does not require any parameter as an input for analyzing point patterns. We show that J'(r) displays a valley shape in the presence of clusters of molecules, and the characteristics of the valley reliably report the clustering features in the data. Most importantly, the position of the J'(r) valley ([Formula: see text]) depends exclusively on the density of clustering molecules (ρc). Therefore, it is ideal for direct estimation of the clustering density of molecules in single-molecule localization microscopy. As an example, this descriptor was applied to estimate the clustering density of ptsG mRNA in E. coli bacteria.

Robust nonparametric quantification of clustering density of molecules in single-molecule localization microscopy.

We present a method for the quantification of small regulatory RNAs (sRNAs) in bacteria, by combining single-molecule fluorescence in situ hybridization (smFISH), super-resolved single-fluorophore microscopy, and clustering analysis. Compared to smFISH imaging with diffraction-limited fluorescence microscopy, our method provides better quantification for short and abundant RNA (such as sRNAs) in a small volume of bacterial cells. Our method can also be directly used for the quantification of messenger RNAs (mRNAs).

Article	Year
The Small Protein SgrT Controls Transport Activity of the Glucose-Specific Phosphotransferase System. Journal of bacteriology\| PubMed ID: 28289085	2017
Robust nonparametric quantification of clustering density of molecules in single-molecule localization microscopy. PloS one\| PubMed ID: 28636661	2017
Quantitative Super-Resolution Imaging of Small RNAs in Bacterial Cells. Methods in molecular biology (Clifton, N.J.)\| PubMed ID: 29484595	2018

Seongjin Park

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