Bacillus subtilis single-stranded DNA-binding protein SsbA is phosphorylated at threonine 38 by the serine/threonine kinase YabT
Background and purpose: Single-stranded DNA-binding proteins participate in all stages of DNA metabolism that involve single-stranded DNA, from replication, recombination, repair of DNA damage, to natural competence in species such as Bacillus subtilis. B. subtilis single-stranded DNA-binding proteins have previously been found to be phosphorylated on tyrosine and arginine residues. While tyrosine phosphorylation was shown to enhance the DNA-binding properties of SsbA, arginine phosphorylation was not functionally characterized.
Materials and methods: We used mass spectrometry analysis to detect phosphorylation of SsbA purified from B. subtilis cells. The detected phosphorylation site was assessed for its influence on DNA-binding in vitro, using electrophoretic mobility shift assays. The ability of B. subtilis serine/threonine kinases to phosphorylate SsbA was assessed using in vitro phosphorylation assays.
Results: In addition to the known tyrosine phosphorylation of SsbA on tyrosine 82, we identified a new phosphorylation site: threonine 38. The in vitro assays demonstrated that SsbA is preferentially phosphorylated by the B. subtilis Hanks-type kinase YabT, and phosphorylation of threonine 38 leads to enhanced cooperative binding to DNA.
Conclusions: Our findings contribute to the emerging picture that bacterial proteins, exemplified here by SsbA, undergo phosphorylation at multiple residues. This results in a complex regulation of cellular functions, and suggests that the complexity of the bacterial cellular regulation may be underestimated.
The contents of PERIODICUM BIOLOGORUM may be reproduced without permission provided that credit is given to the journal. It is the author’s responsibility to obtain permission to reproduce illustrations, tables, etc. from other publications.