Single-strand binding protein
Encyclopedia
Single-strand binding protein, also known as SSB or SSBP, binds to single stranded regions of DNA to prevent premature annealing. 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. Active E. coli 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.
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. Active E. coli 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.
See also
- DNA-binding proteinDNA-binding proteinDNA-binding proteins are proteins that are composed of DNA-binding domains and thus have a specific or general affinity for either single or double stranded DNA. Sequence-specific DNA-binding proteins generally interact with the major groove of B-DNA, because it exposes more functional groups that...
- Nucleic acid simulations