Recognition helices of lac and lambda repressor are oriented in opposite directions and recognize similar DNA sequences.
Exchanges in positions 1 and 2 of the putative recognition helix allow lac repressor to bind to ideal lac operator variants in which base pair 4 has been replaced. We show here that an Arg-22----Asn exchange in position 6 of the putative recognition helix of lac repressor abolishes lac repressor binding to ideal lac operator. This lac repressor variant, however, binds to a variant of the ideal lac operator 5' TTTGAGCGCTCAAA 3' in which the original G.C of position 6 has been replaced by T.A. This result and our previous data confirm our suggestion that the N terminus of the recognition helix of lac repressor enters the major groove close to the center of symmetry of lac operator and that its C terminus leaves the major groove further away from the center of symmetry. The consequences of this model are discussed in regard to various phage and bacterial repressor operator systems.
Lehming
N
N
Institut für Genetik, Universität zu Köln, Federal Republic of Germany.
Sartorius
J
J
Oehler
S
S
von Wilcken-Bergmann
B
B
Müller-Hill
B
B
D001483:Base Sequence; D004269:DNA, Bacterial / Q000032:analysis*; D004268:DNA-Binding Proteins; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010957:Plasmids; D012097:Repressor Proteins / Q000032:analysis*; D014157:Transcription Factors / Q000032:analysis*; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins
D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins