# Mutations upstream from sdaC and malT in Escherichia coli uncover a complex interplay between the cAMP receptor protein and different sigma factors

## TL;DR

The paper explores how mutations in Escherichia coli affect gene regulation, revealing new insights into how bacteria control gene expression during different growth phases.

## Contribution

The study reveals new insights into the interplay between the cAMP receptor protein and sigma factors in bacterial promoters.

## Key findings

- Mutations in Escherichia coli lead to cAMP-independent regulation of malT and sdaC genes.
- The location of the cAMP receptor protein binding site affects sigma factor usage in gene regulation.
- The research provides new understanding of bacterial promoter architecture and gene regulation during growth phases.

## Abstract

In Escherichia coli, one of the best understood microorganisms, much can still be learned about the basic interactions between transcription factors and promoters. When a cAMP-deficient cya mutant is supplied with maltose as the main carbon source, mutations develop upstream from the two genes malT and sdaC. Here, we explore the regulation of the two promoters, using fluorescence-based genetic reporters in combination with both spontaneously evolved and systematically engineered cis-acting mutations. We show that in the cya mutant, regulation of malT and sdaC evolves toward cAMP-independence and increased expression in the stationary phase. Furthermore, we show that the location of the cAMP receptor protein (Crp) binding site upstream of malT is important for alternative sigma factor usage. This provides new insights into the architecture of bacterial promoters and the global interplay between Crp and sigma factors in different growth phases.

This work provides new general insights into (1) the architecture of bacterial promoters, (2) the importance of the location of Class I Crp-dependent promoters, and (3) the global interplay between Crp and sigma factors in different growth phases.