title: Phage lambda repressor revertants. Amino acid substitutions that restore activity to mutant proteins.
abstract: We have isolated same-site and second-site revertants that restore partial activity, wild-type activity, or greater than wild-type activity, to lambda repressor proteins bearing different mutations in the DNA binding domain. In some cases the revertant repressors contain same-site substitutions that are similar to the wild-type side-chain (e.g. Tyr22----Phe, Ser77----Thr). The activity of these revertants makes it possible to assess the role of specific hydrogen bonds and/or packing interactions in repressor structure and function. In other same-site revertants, a very different type of residue is introduced (e.g. Ser35----Leu, Gly48----Asn). This indicates that the chemical and steric requirements at these side-chain positions are relaxed. Two of the second-site revertants, Glu34----Lys and Gly48----Ser, restore activity to more than one primary mutant. Both substitutions apparently increase the affinity of the repressor-operator interaction by introducing new contacts with operator DNA. These results suggest that reversion may be a generally applicable method for identifying sequence changes that increase the activity of a protein to greater than wild-type levels.
mesh_terms: D000595:Amino Acid Sequence; D010582:Bacteriophage lambda / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D007109:Immunity; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics*; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D004279:DNA, Viral; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins