engleski

Single-stranded DNA binding protein has a key role in chromosome segregation during sporulation of Streptomyces coelicolor

Single stranded DNA binding proteins (SSB) o proteins are essential in all domains of life. These proteins bind ssDNA with a high affinity and in a sequence independent manner. Thus SSB proteins protect transiently formed ssDNA during DNA replication, recombination and repair and prevent formation of unproductive secondary structures. In addition, SSB proteins interact and modulate the functions of various proteins involved in all aspects of DNA metabolism. Our recent analysis of all available bacterial genomes revealed the presence of multiple copies of SSB proteins in many bacteria indicating that evolution of these proteins in Eubacteria is highly dynamic. However, the role of duplicated SSB proteins is poorly studied. We have selected multicellular prokaryote, bacterium Streptomyces coelicolor with mycelial life style which also possesses two SSBs, as a good model system to study biological role(s) of paralogous SSB proteins. Differential regulation of paralogous ssb genes in S. coelicolor also suggested that their products have different biological roles. 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 upregulated. Promoters for both genes are determined. Surprisingly, promoter of ssbB possesses unusual features and is active in taxonomically distant Escherichia coli. Results of the gene disruptions strongly indicated that SsbA is essential for survival while SsbB is important during the sporulation process. To get a better insight into the biological role of SsbB and the complex mechanism of cell division in Streptomyces we have constructed double (ssbBparB ; ssbBsmc) and triple (ssbBparBsmc) mutant strains carrying mutations in ssbB gene and in the genes reported previously to be important for the chromosomal segregation. By fluorescence microscopy we examined the effect of these mutations on chromosome segregation during reproductive phase of S. coelicolor.

Streptomyces coelicolor; SSB protein; chromosome segregation

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