Fine-Structure Mapping by Transformation in the Tryptophan Region of Bacillus subtilis

Abstract

The arrangements of eight mutational sites within a segment of the tryptophan cluster of Bacillus subtilis have been determined by three-point reciprocal crosses with a mutation in the same gene cluster used as an outside marker. Estimates of distances between sites were made by two-point crosses and normalization to recombination values for an unlinked marker to correct for physiological variabilities between recipient strains. In general, the additivities of map distances determined by this procedure were reasonable, although some discrepancies were noted in reciprocal crosses between widely separated sites within the gene region examined. No definite polarity effect on recombination was evident, and it appears that the variations observed in reciprocal crosses may be an effect of the probability of recovery of crossovers between exogenotic and endogenotic segments. It is concluded that fine-structure mapping is feasible for the transformation system in this organism and that a high degree of resolution can be attained.