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 naturally want to revert to the double helical form, but SSB binds to the single-strands, keeping them separated, and allowing the DNA replication machinery to perform its function. SSB proteins have been identified in numerous organisms, including humans. The best characterised SSB is that from the bacteria E. coli. Like most bacterial SSBs, it exists as a tetramer under most conditions, 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 differences in the number of subunits of SSB in contact with the DNA.