Abstract
(1) Mutants of phage λ occurred in gene cI which show clear plaque at high temperature but normal turbid plaque at low temperature, were isolated. (2) Lysogens for cItsA are induced irreversibly even at low temperature after heat treatment, and lysogens for λcItsB are induced only when the cultures are heated at a high temperature during growth. These results confirmed those of Lieb (1966) and Horiuchi and Inokuchi (1967). (3) λcItsA and λcItsB mutants were all mapped in the left and right part of gene cI, respectively, as reported by Lieb (1966). (4) Some λcItsB which are located on the right-end region of gene cI complement λcItsA for lysogenization.
