Abstrakt

To study the biochemical properties of SSB from Desulfolatea psychrophila (DpsSSB), we have cloned the ssb genes obtained by PCR and have developed Escherichia coli overexpression systems. The gene consists of an open reading frame of 426 nucleotides encoding SSB protein of 142 amino acids with a calculated molecular mass of 15.6 kDa and it is the smallest known bacterial SSB protein indentified to date. The amino-acid sequence of DpsSSB exhibits 41% identity and 56% similarity to Escherichia coli SSB. In analysis by gel filtration chromatography we show that DpsSSB is functional as homotetramer, with each monomer encoding one single-stranded DNA binding domains (OB-fold). In fluorescence titrations with poly(dT), it binds single-stranded DNA with a binding site size of about 19 - 25 nt depending on the salt concentration, and fluorescence is quenched by about 90%. Thermostability with half-lives of about 15 min at 90°C and 5 min at 100°C makes SSB from Desulfolatea psychrophila the most thermostable SSB protein among psychrophilic and mesophilic bacteria indentified to date. DpsSSB is more thermostable even than SSB from T. aquaticus and T. thermophilus offering an very attractive alternative for theirs in numerous applications in diverse molecular biology and analytical methods.

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