Modification by manganous chloride of the frequency of mutation induced by nitrogen mustard.

HE fact that a posttreatment can abolish the mutations induced by a mutaTgenic agent can furnish a tool for the study of the metabolic conditions that are necessary for the completion of processes that begin with the mutagenic treatment and lead finally to mutation (WITKIN 1956; DOUDNEY and HAAS 1958, 1960). Different agents can produce a decrease in the mutation frequency after UV treatment: visible light (KELNER 1949), chloramphenicol and, in general, conditions inhibiting protein synthesis ( WITKIN 1956), 5-hydroxyuridine (DOUDNEY and HAAS 1960), etc. This type of postirradiation response has also been found with ionizing radiations (KADA, BRUN and MARCOVICH 1960). MORPURGO and SERMONTI (1959) have shown that posttreatment with MnC1, of diploid conidia of Penicillium chrysogenum treated with nitrogen mustard (HN-2) produces reactivation of viability and diminishes induced somatic segregation. The period during which the HN-2 effects are reversible lasts several hours. The present report describes the effect of MnC1, on HN-2-induced mutation in a haploid strain of Penicillium chrysogenum and contains preliminary indications on the postincubation period that is necessary to make the mutations irreversible. Using the terminology of DOUDNEY and HAAS (1958) we have studied the process of “fixation” by means of the “MnCl, challenge” of a mutation induced by HN-2.