engleski

A novel supstrate of bacterial tyrosine kinase

Single stranded DNA binding proteins (SSBs) play an essential role in various stages of DNA metabolism such as replication, recombination and repair. Besides stabilizing single-stranded DNA (ssDNA), SSBs interact with enzymes such as DNA polymerase, RNA polymerase or DNA helicase and modulate their activities. Although bacterial and eukaryotic SSBs differ considerably in their structure these proteins accomplish similar functions in the cells. It is known that eukaryotic SSBs are regulated by phosphorylation on several serine and threonine residues. Until this study phosphorylation of SSB proteins in bacteria has not been recognized. By immunoaffinity chromatography we purified tyrosine phosphorylated Streptomyces griseus SSB. Since genes encoding protein-tyrosine kinases have not been recognized in streptomycetes and SSBs from Streptomyces coelicolor and Bacillus subtilis share 40% identity, we used a B. subtilis protein-tyrosine kinase YwqD to examine phosphorylation of the two cognate SSBs (SSB and YwpH) in vitro. We demonstrate that in vivo phosphorylation of B. subtilis SSB occurs on tyrosine residue 82, and that this reaction is affected antagonistically by B. subtilis tyrosine kinase (YwqD) and phosphatase (YwqE). Phosphorylation of B. subtilis SSB significantly increased binding to single-stranded DNA in vitro. We also found that under DNA-damaging conditions in B. subtilis cells SSB was phosphorylated to a significantly lower extent suggesting that this specific SSB modification might play a role in DNA repair. Further, we observed that tyrosine phosphorylation of B. subtilis, S. coelicolor, and Escherichia coli SSBs occured while they were expressed in E. coli. These results indicate that tyrosine phosphorylation of SSBs is a conserved process of post-translational modification in taxonomically distant bacteria.

bacterial tyrosine kinase; SSB

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