title: Cloning and characterization of the natural lactose operator.
abstract: A 55-bp DNA segment carrying the wild-type lactose operator sequence has been cloned. Its sequence is: (Formula: see text). With the exceptions of the bases at positions 19 and 41, 26 and 34, and 28 and 32, the sequence is a perfect inverted repeat about base pair 30. This segment was obtained from the wild-type lactose promoter and operator region of lambda h80dlac phage DNA by a combination of in vitro and in vivo steps. Up to four direct-repeat copies of this segment have been cloned in plasmid pMB9 and pBR325. Repressor affinity for this 55-bp fragment does not differ significantly from that for a 40-bp synthetic operator fragment cloned previously, even though the 55-bp fragment contains the complete set of sequence symmetries associated with the natural operator, whereas the 40-bp fragment does not. An improved procedure for operator purification is described: this was used to prepare 14 mg of the 55-bp fragment over a 2-month period.
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics; D001483:Base Sequence; D003001:Cloning, Molecular / Q000379:methods; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics*; D004274:DNA, Recombinant / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D007763:Lac Operon; D009876:Operon; D010957:Plasmids; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D004274:DNA, Recombinant; D012097:Repressor Proteins; D004262:DNA Restriction Enzymes