Some precursors of the 5-hydroxymethylcytosine of T6r+ bacteriophage.

A new pyrimidine, 5-hydroxymethylcytosine (HMC) (1, 2), has been isolated from bacterial viruses of the T even type, which multiply in Escherichia coli. Deoxyriboside (3) and deoxyribotide (4) derivatives from this source have also been described. These components are not present in appreciable quantities in the nucleic acids of E. coli or of other cells, or in any other virus analyzed to date. Cytosine is completely absent from the T even viruses, being replaced by HMC in the deoxyribonucleic acid (DNA), the sole nucleic acid of these viruses. This report presents some data on the origin of the hydroxymethyl group as well as the ring of this new compound. In earlier studies on the biosynthesis of the pyrimidine ring itself (5), the bacterial host pyrimidines were first labeled independently of the purines by growth in C4-labeled erotic acid. After multiplication of T6r+ bacteriophage in this pyrimidinelabeled host in the absence of exogenous erotic acid, it was found that the resulting progeny contained labeled pyrimidines. This demonstrated the utilization of host DNA to form pyrimidines of the virus, since it had been shown that preformed ribonucleic acid (RNA) is inert in the virus-infected cell (6, 7). The pyrimidine bases were isolated from DNA in the form of the deoxyribonucleotides and characterized by their chromatographic properties and ultraviolet absorption spectra. From these properties it was considered that nucleotides of thymine and cytosine had been isolated from the virus. As described elsewhere (4), a thymine-containing nucleotide had been correctly identified, but the substance thought to contain cytosine proved to be a combination of nucleotides of HMC and thymine with various properties quite similar to those of a diphosphonucleotide of cytosine. Accordingly, studies have been repeated and extended on the origin of the pyrimidines of T6r+, improved methods for the isolation and characterization of the nucleotides and the free bases being used.