Biological activity of 5-hydroxymethyluracil and its deoxynucleoside in noninfected and phage-infected Bacillus subtilis

Biosynthesis of 5-(4'5'-dihydroxypentyl) uracil as a nucleoside triphosphate in bacteriophage SP15-infected Bacillus subtilis

The nucleoside triphosphate of 5-(4',5'-dihydroxypentyl)uracil (DHPU) was detected in the acid-soluble extract from bacteriophage SP15-infected Bacillus subtilis W23. No uracil was found in the DNA of either replicating or mature phage. Labeled thymidine added during phage DNA synthesis was incorporated into phage DNA. The presence of DHPU as a nucleoside triphosphate in the acid-soluble pool and the incorporation of thymidine into phage DNA suggest that both DHPU and thymine are incorporated into SP15 DNA via their nucleoside triphosphates. 5-Fluorodeoxyuridine inhibited biosynthesis of SP15 DNA, and this inhibition was reversed by thymidine, resulting in the synthesis of a DNA containing reduced amounts of fully modified DHPU. It is proposed that 5-fluorodeoxyuridine, or its metabolic product, inhibits a step in the biosynthetic pathway to the nucleoside triphosphate of DHPU.

Bacteriophages of Bacillus subtilis

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Synthesis of the unusual DNA of Bacillus subtilis bacteriophage SP-15

Cultures of Bacillus subtilis infected with phage SP-15 were examined to investigate the metabolic origin of two of the unique components of the phage DNA: the component responsible for the unusually high buoyant density in CsCl and the unusual pyrimidine, 5-(4', 5'-dihydroxypentyl) uracil (DHPU). Newly synthesized pulse-labeled DNA was light in buoyant density and shifted to the high density of mature phage DNA upon further incubation. Parental DNA was converted to a light-density intermediate form prior to replication. When labeled uracil, thymidine, or DHPU were added to infected cells, it was found that only uracil served as the precursor to DHPU and thymine in phage DNA. Analysis of the bases from hydrolyzed DNA of labeled phage or infected cells indicated that the uracil was incorporated into the DNA as such (presumably via deoxyuridine triphosphate) and later converted to DHPU and thymine at the macromolecular level. The sequence of events after phage infection appeared to be: (i) injection of parental DNA; (ii) conversion of parental DNA to a light form; (iii) DNA replication, yielding light DNA containing uracil; (iv) conversion of uracil to DHPU and thymine; and (v) addition of the heavy component.

Dominance relationships in mixedly infected Bacillus subtilis

The progeny released from Bacillus subtilis cells mixedly infected with bacteriophages beta22, SP82, and SP02(c1) have been studied at varying multiplicities of infection and orders of addition and with different host strains of the bacterium. In B. subtilis 168, SP02(c1) was subordinate to both SP82 and beta22 and did not yield significant numbers of progeny even when added 5 min before the superior phage. Dominance in mixed infections of beta22 and SP82 was host-dependent. In B. subtilis 168, SP82 was dominant and greatly reduced the yield of beta22 if added simultaneously or before the subordinate partner. However, in the same mixed infection in B. subtilis SB11, beta22 was the dominant phage and totally suppressed the production of SP82 even when added 5 min after the latter.