# Regulatory Role of GgaR (YegW) for Glycogen Accumulation in Escherichia coli K-12

## TL;DR

The paper identifies a protein, GgaR, that controls glycogen storage in E. coli based on glucose availability.

## Contribution

The study reveals that GgaR (YegW) is a glucose-sensing transcriptional repressor regulating glycogen accumulation in E. coli.

## Key findings

- YegW (GgaR) is a single-target transcription factor that represses the yegTUV operon.
- GgaR represses glycogen accumulation in response to glucose levels, independent of growth phase.
- E. coli lacking GgaR accumulates more glycogen but grows poorly in low-glucose conditions.

## Abstract

Glycogen, the stored form of glucose, accumulates upon growth arrest in the presence of an excess carbon source in Escherichia coli and other bacteria. Chromatin immunoprecipitation screening for the binding site of a functionally unknown GntR family transcription factor, YegW, revealed that the yegTUV operon was a single target of the E. coli genome. Although none of the genes in the yegTUV operon have a clear function, a previous study suggested their involvement in the production of ADP-glucose (ADPG), a glycogen precursor. Various validation through in vivo and in vitro experiments showed that YegW is a single-target transcription factor that acts as a repressor of yegTUV, with an intracellular concentration of consistently approximately 10 molecules, and senses ADPG as an effector. Further analysis revealed that YegW repressed glycogen accumulation in response to increased glucose concentration, which was not accompanied by changes in the growth phase. In minimal glucose medium, yegW-deficient E. coli promoted glycogen accumulation, at the expense of poor cell proliferation. We concluded that YegW is a single-target transcription factor that senses ADPG and represses glycogen accumulation in response to the amount of glucose available to the cell. We propose renaming YegW to GgaR (repressor of glycogen accumulation).