Amino Acid Replacements Associated with Mutation and Recombination in the A Gene and Their Relationship to In Vitro Coding Data

Studies on mutational alteration of protein structure showed that seven different amino acids could occupy one position in the A protein of the tryptophan synthetase of Escherichia coli (Helinski and Yanofsky, 1962; Henning and Yanofsky, 1962a, 1962b; Carlton and Yanofsky, 1963). Two distinguishable mutants were isolated initially, strains A-23 and A-46, in which amino acid replacements had occurred at the same position in the A protein. Revertants were then obtained from each of these mutants and the reversion events were found to be associated with other amino acid changes. These amino acid changes and the amino acid sequence of the relevant region of the A protein are shown in Fig. 1. Since the changes detected at the one position in the A protein are mutationally related, it should be possible to employ this material in an investigation of the in vivo relationships between the coding units corresponding to the seven...