Single stranded binding protein: Difference between revisions

SSB proteins have been identified in many different organisms, but the most well understood SSB remains the SSB of ''E. coli''.  ''E. coli'' SSB is a homotetramer consisting of <scene name='56/566528/Homotetramer/1'>four identical subunits</scene> which are each about 19 kDa in size <ref>PMID:2087220</ref>.  There are two different binding modes of the ''E. coli'' SSB when it complexes with ssDNA<ref>PMID:11993998</ref>.  Regulation of these modes has been found to be dependent on salt concentration, in addition to other unknown factors.  Under low salt conditions, the protein is less efficient as only two of the four identical subunits of ''E. coli'' SSB were found to bind to the ssDNA <ref>PMID:11993998</ref>. This is a common theme among DNA binding proteins. The cause is presumed to be that the protein has less ion decoration at lower salt levels. And it could be that the subunits interact with each other through salt bridges to remain close to each other and the DNA. Under high salt concentrations, however, all four subunits of the homotetramer bind to the ssDNA, increasing the number of nucleotides in contact with the SSB and thus favoring SSB-ssDNA interactions.  Depending on the salt concentration and other factors, estimates of the size of the site of interaction between SSB and ssDNA range anywhere from 30 to 73 nucleotides for each tetramer <ref>PMID:11993998</ref>.   

</StructureSection>