A developmentally regulated Caulobacter flagellar promoter is activated by 3' enhancer and IHF binding elements

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Genetics

Background:

• Flagellar gene transcription in Caulobacter crescentus is tightly regulated during the cell cycle.
• Specific cis-regulatory elements, including sigma 54 promoters, integration host factor (IHF) binding sites, and ftr enhancer elements, are shared by these genes.

Purpose of the Study:

• To investigate the role of cis-regulatory elements in the temporal and spatial regulation of flagellar gene transcription.
• To characterize the proteins binding to the ftr enhancer sequences and the Caulobacter homolog of IHF.

Main Methods:

• Partial purification of ftr-binding proteins and Caulobacter IHF.
• In vitro assays for protein binding and lambda recombination.
• Site-directed mutagenesis to assess the in vivo function of enhancer and IHF binding sites in the flaNQ gene.

Main Results:

• Ftr-binding proteins require enhancer sequences for binding, correlating with transcriptional activation.
• Caulobacter IHF facilitates in vitro integrase-mediated lambda recombination.
• In vivo studies demonstrate that 3' enhancer and IHF binding elements are essential for flaNQ operon transcription.
• IHF and ftr-binding proteins are localized to predivisional cells, and flaNQ promoter expression is polar.

Conclusions:

• The study provides the first in vivo evidence for the requirement of 3' enhancer and IHF binding elements in bacterial gene transcription.
• The temporal and polar expression of flagellar genes suggests a common regulatory mechanism involving IHF and ftr-binding proteins.