engleski

How SSB protein ensures sporulation in dominant soil bacteria

Single-stranded DNA binding (SSB) proteins are essential for all domains of life. These proteins have an important role in all processes of DNA metabolism due to their abilities (i) to bind and protect single stranded DNA, (ii) to interact and modulate the functions of other proteins involved in DNA replication, repair and recombination. Our results showed that many bacteria possess more than one gene encoding this protein. Paralogous SSBs often differ in size and the cellular role of additional copy of ssb gene(s) is not well understood. Streptomycetes are saprophytic bacteria and the largest genus of Actinobacteria. These bacteria are abbundantly present in soil and exhibit complex life cycle resembling those of eukaryotes. Harsh growing condition in the soil and dispersion is achived by spore formation. Their genomes are large, containing great number of genes, especially those involved in regulation and signaling. Streptomycetes possess two ssb genes. The functions of proteins encodied by these genes, SsbA and SsbB, have not been studied so far. We demonstrated that in Streptomyces coelicolor two ssb genes 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 gene is significantly up regulated. Promoters for both genes are determined. Surprisingly, promoter of ssbB gene possesses unusual features. Both genes were disrupted on the genome and our results strongly suggested that SsbA is essential for survival while SsbB protein in S. coelicolor is important for chromosome segregation into the spores.

SSB proteins; DNA replication; repair and recombination; Streptomyces coelicolor; chromosome segregation

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