The adnAB locus, encoding a putative helicase-nuclease activity, is essential in Streptomyces

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Homologous recombination repairs DNA double-strand breaks (DSBs) via DNA end resection.
• Multisubunit helicase-nuclease complexes like E. coli RecBCD initiate this process.
• Homologues of RecBCD (AddAB) are found in B. subtilis and M. tuberculosis (AdnAB).

Purpose of the Study:

• To investigate the DNA repair mechanisms in Streptomyces.
• To identify the helicase-nuclease complex responsible for DNA double-strand break repair in Streptomyces.
• To determine the essentiality and function of the identified genes in DNA damage resistance.

Main Methods:

• Bioinformatic analysis of Streptomyces genomes to identify homologous genes.
• Gene disruption experiments in Streptomyces ambofaciens and Streptomyces coelicolor.
• Inducibility studies using mitomycin C.
• Complementation experiments by introducing Streptomyces adnAB into an E. coli recB mutant.

Main Results:

• Streptomyces genomes lack recBCD and addAB homologues but possess adnAB genes, homologous to M. tuberculosis adnAB.
• adnAB genes are essential for growth in Streptomyces and are conserved as single copies.
• Streptomyces adnA and adnB genes are inducible by DNA damage and independently transcribed.
• Expression of S. ambofaciens adnAB in an E. coli recB mutant restored viability and UV resistance.

Conclusions:

• Streptomyces AdnAB is a functional homologue of E. coli RecBCD, essential for DNA double-strand break repair and growth.
• Streptomyces AdnAB plays a critical role in DNA damage resistance.
• The AdnAB complex represents a conserved mechanism for DNA repair across diverse bacterial species.