BIOSYNTHESIS OF NUCLEIC ACID IN ESCHERICHIA COLI

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Abstract
By means of isotopic tracer methods which take advantage of the nutritional characteristics of growing bacteria, it is possible to determine which substances serve as sources of nucleic acid carbon. It is also possible to insert suspected precursors at various places along the synthetic streams which form nucleic acid and to decide what parts they play while contributing to the flow of C. Thus studies using media supplemented by pyrimidine nucleosides specify some of the processes involved in the synthesis of nucleic acid. In these cases the purines are manufactured from glucose-carbon, while the ribose associated with them is derived from the externally supplied pyrimidine nucleoside. This transfer of ribose involves a process much like, and perhaps identical with, transglycosidation. Meanwhile, the pyrimidine nucleosides are also incorporated into nucleic acid as units. The same mechanisms operate when pyrimidine nucleotides are studied. Here, however, the P of the nucleotide is replaced by P derived from the inorganic P of the medium. Although the exact nature of the mechanism which inserts P into nucleic acid has not been revealed, we would suggest that P compounds, perhaps of the uridine-tri-phosphate type, react with nucleosides to form the nucleic acid linkages in ribonucleic acid chains.