Quaternary structure and function in phage lambda repressor: 1H-NMR studies of genetically altered proteins.
The quaternary structure and dynamics of phage lambda repressor are investigated in solution by 1H-NMR methods. lambda repressor contains two domains separable by proteolysis: an N-terminal domain that mediates sequence-specific DNA-A binding, and a C-terminal domain that contains strong dimer and higher-order contacts. The active species in operator recognition is a dimer. Although the crystal structure of an N-terminal fragment has been determined, the intact protein has not been crystallized, and there is little evidence concerning its structure. 1H-NMR data indicate that the N-terminal domain is only loosely tethered to the C-terminal domain, and that its tertiary structure is unperturbed by proteolysis of the "linker" polypeptide. It is further shown that in the intact repressor structure a quaternary interaction occurs between N-terminal domains. This domain-domain interaction is similar to the dimer contact observed in the crystal structure of the N-terminal fragment and involves the hydrophobic packing of symmetry-related helices (helix 5). In the intact structure this interaction is disrupted by the single amino-acid substitution, Ile84----Ser, which reduces operator affinity at least 100-fold. We conclude that quaternary interactions between N-terminal domains function to appropriately orient the DNA-binding surface with respect to successive major grooves of B-DNA.
Weiss
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Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139.
Karplus
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Sauer
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RT
D010582:Bacteriophage lambda / Q000235:genetics*; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology; D014764:Viral Proteins / Q000235:genetics
D046911:Macromolecular Substances; D012097:Repressor Proteins; D014157:Transcription Factors; D014764:Viral Proteins