FIGURE 2. A map of the relative positions of e mutants described in this study. Mutants with the prefix J were induced by proflavine; mutants with the prefix JD are spontaneous mutants isolated from pseudowild strains. The map is not drawn to scale. two types of mutants: one identical to the original mutant, the other a new mutant. A map of the relative positions of the mutations utilized in this study is given in Fig. 2. The lysozyme from bacteria infected with wildtype phage and with each of the pseudowild strains was purified, oxidized, and digested with trypsin, and the digest was chromatographed on Dowex 50-X2 resin (Terzaghi et al., 1966). In each case the mutant lysozyme was found to differ from the wild-type in one or two peaks out of a total of 18. The sequence of amino acids in the changed region of the wild-type lysozyme and in each of the mutant lysozymes was determined. Using triplets proposed by Khorana and Nirenberg, it was possible in each case to assign a sequence of bases that could code for the wild-type sequence of amino acids and that, with the proper addition and/or deletion of bases, could code for the changed sequence of amino acids in the mutant strains. Table 1 shows the sequences of amino acids, and the related base sequences for the lysozymes of the mutant strains analyzed.