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Chapter 25 : Gene Transfer out of the Microbial World
The study of Bacillus subtilis transformation might be more fruitful than a continuation of the investigation on Escherichia coli. This was an important decision for a postdoc who would be looking for a job in a few years. Joshua and Esther Lederberg determined that genes of tryptophan synthesis were closely linked to a gene of histidine biosynthesis. More extensive analysis of this region demonstrated that additional genes of aromatic acid biosynthesis were closely linked to each other and to the his locus. They also identified a new form of allosteric inhibition of aromatic acid synthesis and published a number of papers on the genetics, biochemistry, and regulation of the pathway. The author also focused on studying the mechanism by which donor DNA is taken up by competent cells of B. subtilis. The author also focused on Agrobacterium and the disease that it caused in plants, crown gall tumors, for a number of reasons, all of which seem to have crystallized simultaneously. From the very beginning, Joshua and Esther Lederberg believed that Schilperoort was correct in concluding that DNA was transferred from Agrobacterium into plant cells. Using techniques of DNA-DNA hybridization, they demonstrated that many strains of Agrobacterium that were not lysogenic for this phage nevertheless caused crown gall tumors.