Bacterial single-stranded DNA-binding proteins are phosphorylated on tyrosine

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Single-stranded DNA-binding proteins (SSBs) are crucial for DNA metabolism in all organisms.
• Eukaryotic SSBs are regulated by serine/threonine phosphorylation, but bacterial SSB phosphorylation was uncharacterized.
• Bacterial tyrosine kinases were investigated as potential regulators of SSBs.

Purpose of the Study:

• To investigate the phosphorylation of bacterial single-stranded DNA-binding proteins (SSBs).
• To identify the specific residues and enzymes involved in bacterial SSB phosphorylation.
• To determine the functional consequences of SSB phosphorylation on DNA binding.

Main Methods:

• Immunoaffinity chromatography was used to identify phosphotyrosine-containing proteins in Streptomyces griseus.
• Bacterial protein-tyrosine kinase YwqD from Bacillus subtilis was used to phosphorylate SSBs in vitro.
• In vivo and in vitro assays were performed to analyze SSB phosphorylation and DNA-binding affinity.

Main Results:

• Bacterial SSBs were identified as novel targets of bacterial tyrosine kinases.
• In vivo phosphorylation of Bacillus subtilis SSB occurred on tyrosine residue 82, regulated by kinase YwqD and phosphatase YwqE.
• Phosphorylation increased the DNA-binding affinity of Bacillus subtilis SSB to single-stranded DNA by nearly 200-fold.
• Tyrosine phosphorylation of SSBs was conserved across taxonomically distant bacteria (B. subtilis, S. coelicolor, E. coli).

Conclusions:

• Tyrosine phosphorylation is a novel and conserved post-translational modification of SSBs in bacteria.
• This phosphorylation significantly enhances the DNA-binding ability of SSBs.
• The findings reveal a new regulatory mechanism for DNA repair, recombination, and replication in bacteria.