engleski

Implication of Single Stranded DNA Binding Protein in Chromosome Segregation during Reproductive Growth of Streptomyces coelicolor

Single stranded DNA binding proteins (SSB) proteins are essential for cell survival. SSB proteins, identified in all domains of life, exhibit their role through binding and protecting single stranded DNA. During DNA replication, recombination and repair SSB proteins interact and modulate the functions of various proteins involved in all aspects of DNA metabolism. Comprehensive analysis of SSB interactions in E. coli and B. subtilis showed its prominent role in the complex protein network responsible for genome maintenance. Our recent bioinformatics analysis of all available bacterial genomes revealed presence of the ssb parologues in many bacteria. In addition, these results indicated that evolution of SSB proteins in Eubacteria is highly dynamic. However the role of duplicated ssb genes is poorly studied. Therefore, in this study we selected Streptomyces coelicolor, bacterium with complex life style that also possesses two SSBs, as a good model system to study biological role(s) of paralogous SSB proteins. We demonstrated that two ssb genes in S. coelicolor are differentially regulated. Expression of ssbA is constant and high during life cycle, decreasing towards late stationary phase, while the expression of ssbB is at all-time low. In minimal medium the ssbB is significantly up regulated. Promoters for both genes are determined. Surprisingly, promoter of ssbB possesses unusual features and is active in taxonomically distant bacteria, Escherichia coli. Both genes were disrupted on the genome and our results showed that SsbA is essential for survival while SsbB is important during sporulation process. The 3D structure of SsbB was solved, showing an interesting variation in comparison to quaternary structure of the previously published S. coelicolor SsbA protein. To the best of our knowledge this is the first example of solved crystal structures of two paralogous SSB proteins from the same organism.

paralogous SSB proteins; DNA metabolism; sporulation; Streptomyces

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