Functionally acceptable substitutions in two α‐helical regions of λ repressor

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Abstract
A method of targeted random mutagenesis has been used in investigate the informational content of 25 residue positions in two α-helical regions of the N-terminal domain of λ repressor. Examination of the functionally allowed sequences indicates that there is a wide range in tolerance to amino acid substitution at these position. At position that are buried in the structure, there are severe limitations on the number and type of residues allowed. At most surface positions, many different residues and residue types are tolerated. However, at several surface positions there is a string preference for hydrophilic amino acids, and at one surface position proline is absolutely conserved. The results reveal the high level of degeneracy in the information that specifies a particular protein fold.