Met repressor sandbox (Beasley): Difference between revisions

The met operators in ''E. coli'' consist of tandem repeats of eight base pair sequences, AGACGTCT, with each sequence known as a <scene name='Met_repressor_sandbox_(Beasley)/Met_box/1'>'met box'</scene>. <ref name="Phillips,S" /> These met boxes vary in length from 16-40 base pairs, corresponding to two to five met boxes. The consensus sequence is highly symmetrical, with centers of inverted repeats at the center of each met box and at the junctions between them. The <scene name='Met_repressor_sandbox_(Beasley)/Just_dna/2'>self complementary 19-base oligonucleotide</scene>, that the met repressor binds to in the E. coli met repressor-operator complex at the top of the page, has the sequence 5'-TT '''AGACGTCT''' '''AGACGTCT''' A-3' which contains two tandem consensus met boxes (the met boxes are in bold).<ref name="Phillips">PMID 1406951</ref> One of the products of the methionine biosynthetic pathway is <scene name='Met_repressor_sandbox_(Beasley)/Sam/5'>S-adenosylmethionine (SAM)</scene> and it acts as a corepressor. The met repressor has to bind two molecules of SAM non-cooperatively because the free repressor (aporepressor) has a low affinity for DNA.<ref name="Phillips" /> The SAM binding does not significantly change the structure of the protein, but it greatly increases the affinity for the operator. <ref name="Phillips,S" /> Sam binds to the faces of the repressors, away from the DNA, with interaction between the met repressor and SAM coming from the positively charged sulphur atoms lying at the carboxy termini of the B helices <ref name="Phillips" /> The following image represents SAM: