MUTATIONS RESULTING FROM THE TRANSFORMATION OF <i>BACILLUS SUBTILIS</i>

Abstract

U N E Q U A L crossing over was first proposed by DEMEREC (1962) to explain an increase in reversion rate in Salmonella typhimurium when transduced with phages carrying the same mutation. MAGNI (1963, 1964) found increases in reversion and forward mutation rates in yeast during meiosis as compared with those occurring in mitotic cells. MAGNI and associates (1964) provided evidence that the great majority of revertants occurring during meiotic processes are associated with chromosomal exchange in the region of the mutated locus. By studying spontaneous reversions of T4 r l l mutants of various origins, STRIGINI (1965) found that recombinations of outside markers were related to reversion of proflavin-revertible spontaneous mutants. However, recombinations were not related to reversions of mutations induced by 5-bromouracil. This led to the hypothesis that reverse mutations occur as a consequence of unequal crossing over which causes base losses or insertions in DNA. Base losses and insertions have also been proposed to explain the mutagenic actions of acridine dyes (CRICK et al. 1961; LERMAN 1964). Intact DNA molecules are integrated into the host chromosome in Bacillus subtilis transformation systems (SZYBALSKI 1961 ; PENE and ROMIG 1964; BODMER and GANESAN 1964). There is some direct physical evidence for single strand integration in both B. subtilis and pneumoccocus (BODMER and GANESAN 1964; Fox and ALLEN 1964). Transformations provide a unique opportunity for studying directly the associalion of mutation to recombination even though the mechanisms of integration are not known. The present report describes increases in forward and reverse mutations during transformation of B. subtilis and suggests a direct association of mutation to recombination. The kinetics of transformation and mutation and the calculation of true mutation frequency are also discussed.