抄録
(1) Three different thiazole-less mutants responded to cystine moderately, but one of which, mutant 26-43,responded, though barely measurably, to isoleucine, valine, serine, threonine, histidine and proline also. Mutants 70-17 and 70-23,the former responding to either pyrimidine or thiazole and the latter to intact thiamine only, were permitted to grow to a certain extent by cystine and isoleucine. On the other hand, mutant 283 which required either cystine or isoleucine did not respond to thiazole. (2) The combination of thymine and uracil was able to support the growth of a pyrimidine-less mutant 70-17. (3) It seems improbable that γ-aceto-γ-mercapto-propanol is involved in the normal thiazole synthesis of E.coli. (4) The activity of thiazole-less mutant 26-43 to couple thiamine pyrimidine and thiazole is comparable to that of it's parent E.coli ATCC 9637. The coupling activity of mutant 70-23 seems to be blocked absolutely and that of mutant 70-17 partially. The fact that mutant 70-17 responded to either pyrimidine or thiazole is explainable by the inability to synthesize enough thiamine from the pyrimidine and the thiazole, which have been synthesized by the organism. (5) Evidence was obtained to show that pyrimidine and thiazole moieties of thiamine are actually normal precursors of that growth factor in E.coli.
