ANTAGONISMS BETWEEN PURINES AND PURINE ANALOGUES IN AUXOTROPHS OF SALMONELLA TYPHIMURIUM1

A number of bacterial strains have been used to study the interactions between purines and their structural analogues (Roblin, 1954; Elion, Singer, and Hitchings, 1954; Mandel, 1959; Anderson and Law, 1960). Those strains with specific requirements for purines have been especially useful in such analyses (Collier and Huskinson, 1957). In all of these studies, the structural analogues, acting as inhibitors, have been analyzed in terms of competitive and non-competitive interactions with the growth-promoting purines. The discovery of a specific guanine-requiring mutant of Salmonella typhimurium has provided a particularly unique system for an extended study of the interactions of several purine analogues. With this organism, 2, 6-diamino-purine, an analogue which is normally an in-hibitor of growth, serves as an efficient growth factor. Under such conditions of growth, it was found that a natural purine, adenine, and a structural analogue of guanine, 8-azaguanine, become powerful inhibitors. Furthermore, the growth inhibited by 8-azaguanine can be restored by 6-mercaptopurine, an analogue which normally shows a strong inhibitory action against the prototrophic wild type. The mutant was also found useful in comparing relative com-petitive effectiveness of other adenine-like analogues with diaminopurine. Other mutants were used for the purposes of comparison. A description of these events and analysis of these interactions form the subject of this paper