Heat and DNA damage induction of the LexA-like regulator HdiR from Lactococcus lactis is mediated by RecA and ClpP

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Genetics

Background:

• The SOS response is a key bacterial DNA damage repair mechanism, typically regulated by LexA.
• Some bacteria, like Lactococcus lactis, lack a LexA homologue, suggesting alternative regulatory pathways exist.

Purpose of the Study:

• To identify and characterize the DNA damage response regulator in Lactococcus lactis.
• To elucidate the mechanism of gene expression induction under DNA damage and heat shock in this organism.

Main Methods:

• Gel mobility shift assays to determine HdiR binding sites.
• In vitro self-cleavage assays at varying pH.
• In vivo studies involving DNA-damaging agents and protease activity.
• RecA and Clp protease dependency analysis.

Main Results:

• Identified HdiR as a negative transcriptional regulator in Lactococcus lactis.
• HdiR undergoes RecA-dependent self-cleavage upon DNA damage and Clp protease-mediated degradation.
• The N-terminal cleavage product of HdiR remains DNA-bound, with degradation required for gene induction.
• Both DNA damage and heat shock induce HdiR regulon expression through shared regulatory elements.

Conclusions:

• HdiR activity is regulated by a novel sequential proteolysis mechanism involving self-cleavage and ClpP degradation.
• This pathway represents a unique bacterial stress response independent of the canonical LexA-regulated SOS system.
• Common regulatory elements govern both DNA damage and heat-induced responses mediated by HdiR.