Single-strand binding protein
- Single-strand binding protein
Single-strand binding protein, also known as SSB or SSBP, binds single stranded regions of DNA to prevent premature reannealing. The strands have a natural tendency to revert to the duplex form, but SSB binds to the single strands, keeping them separate and allowing the DNA replication machinery to perform its function.
SSB proteins have been identified in organisms from viruses to humans. While many phage and viral SSBs function as monomers and eukaryotes tend to encode heterotrimeric RPA (Replication Protein A), the best characterized SSB is that from the bacteria "E. coli" which, like most bacterial SSBs exists as a tetramer. An active SSB is composed of four identical subunits, each with a molecular weight of 18 843 Da. Binding of single-stranded DNA to the tetramer can occur in different "modes", with SSB occupying different numbers of DNA bases depending on a number of factors, including salt concentration. For example, the (SSB)65 binding mode, in which approximately 65 nucleotides of DNA wrap around the SSB tetramer and contact all four of its subunits, is favoured at high salt concentrations "in vitro". At lower salt concentrations, the (SSB)35 binding mode, in which about 35 nucleotides bind to only two of the SSB subunits, tends to form. Further work is required to elucidate the functions of the various binding modes "in vivo".
ee also
* DNA-binding protein
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single-strand binding protein — single strand binding protein. См. белок. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
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