THE INDUCTION OF THYMINE SYNTHESIS BY T2 INFECTION OF A THYMINE REQUIRING MUTANT OF ESCHERICHIA COLI

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Abstract
The growth requirements of a thymine-requiring mutant of E. coli, strain 15, are descr. The organism, 15T-, will not multiply in absence of thymine and excretes a uracil-like compound during growth. Strain 15T- loses the ability to produce colonies if maintained in a synthetic medium containing a C source in the absence of thymine. Substances which will prevent loss of viability but which will not permit multiplication, were detected in broth and in media in which 15T- had grown. The organism adsorbs T2 very slowly if grown on a synthetic medium and considerably better when grown in nutrient broth, even when adsorption of both is tested in the same synthetic medium. Virus multiplication may occur in media in the presence or absence of thymine, and the virus produced has the superficial biological attributes of T2. Prepns. of T2r+ virus, isolated from cells infected in the presence or absence of thymine, are chemically identical. They possess a composition similar to that obtained from infected strain B. The thymine content of these virus prepns. exceeds that in the host cell at the beginning of the expt. Cells infected in the absence of thymine synthesize desoxyribo-nucleic acid as rapidly as cells infected in the presence of added thymine. Base analysis of the infected cells shows a net synthesis of thymine, hydroxymethylcystosine, adenine, and guanine. The pyrimidines of virus desoxyribonucleic acid do not appear to be synthesized in the uninfected cells. The ratio of the rates of synthesis of these bases in infected cells is fairly close to the ratios of the molar proportions of the bases existing in virus. This finding is interpreted to signify that the only nucleic acid being accumulated in infected cells is virus desoxyribonucleic acid.