Abstract
The various isoleucine-valine mutants obtained through ultraviolet irradiation have been tested for reversion induction by nitrous acid and by ultraviolet light irradiation. The mutants can be classified into three categories: (1) those which can be induced to revert by both nitrous acid and ultraviolet light, (2) those which can be induced to revert by ultraviolet and not by nitrous acid, and (3) those mutants which cannot be induced to revert either by nitrous acid or ultraviolet light. Three of the isoleucine-valine requiring mutants produce half revertants in addition to full revertants. Depending upon the strain, the half revertants require one of the two amino acids for growth. From a particular strain only one kind of half revertants are obtained, i.e. they require either isoleucine (as in the case of half revertants from M-14 and Nr-211-laM) or valine (as in the case of half revertants from M-12 growth. Another mutant (M-11) produces revertants which are sensitive to valine—the valine inhibition can be overcome by isoleucine.
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