Pyrimidine‐Ribonucleotide Pools and Their Turnover in Phage T4‐Infected Escherichia coli Cells

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Abstract
Exogenous uracil was shown to be taken up efficiently into ribonucleotide pools at all times during the cycle of T4 phage infection, in which stable host RNA synthesis is known to be turned off. This uptake was shown to be effected by ribonucleotide pool expansion and a net increase in mRNA content after phage infection. By comparing different phage mutants, the draining of ribonucleotide pools into DNA synthesis by ribotide reduction, was also found to be instrumental for pool labeling from exogenous uracil. The UDPG pool expanded as much as 3‐fold during DNA negative mutant infection, presumably as a result of absent DNA glucosylation.From measurements of specific activities of nucleotides by double labeling and thin‐layer chromatography, it was concluded that the incorporation into RNA of a radioactive, exogenous base can be reliably used for following T4 phage transcription.