title: How lac repressor recognizes lac operator.
abstract: Nucleotide analogs were substituted for unmodified nucleotides at specific sites in the lac operator sequence by a combination of chemical and enzymatic procedures. The nitrocellulose filter assay was used to study the interactions of these modified operators with wild-type (SQ) and tight-binding (QX86) lac repressors. These studies implicate directly the 5 methyl of thymine and the 2 amino of guanine as important operator-repressor contact sites. Furthermore, when these findings are combined with published results from other laboratories, a model for the lac operator-lac repressor interaction can be derived. Two important postulates follow from this model. (i) The repressor interacts at specific and defined sites with the N7 of guanine, the 5 methyl of thymine, the 2 amino of guanine, and the central major groove of the operator. (ii) The repressor binds to one side of the operator.
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D007763:Lac Operon; D008954:Models, Biological; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D012097:Repressor Proteins; D014157:Transcription Factors