Incorporation of the carbon skeleton of adenosine into the purine nucleosides of ribonucleic acid and deoxyribonucleic acid by Neurospora.

In a previous study (l), evidence was presented to show that in a mutant of Neurospora the whole carbon skeleton of cytidine is incorporated with equal effectiveness into the pyrimidine nucleosides of ribonucleic acid and deoxyribonucleic acid. In this article a comparable experiment is described in which uniformly labeled Cr4-adenosine was fed to an adenine-requiring mutant grown in the presence of sucrose. The purine nucleosides of RNA1 and DNA were all equally labeled. Although the purine nucleosides recovered from the RNA had a distribution of labeling between the purine and the ribose which differed from that of the adenosine fed, the same pattern of labeling was found in the purine deoxyribonucleosides from the DNA. This finding is interpreted to mean that, although some splitting of the administered purine ribonucleoside occurs in its conversion into a ribonucleosyl precursor of the purine nucleosides of RNA, the same ribonucleosyl precursor serves as the intermediate for the formation of the purine deoxyribonucleosides of the DNA. Inasmuch as the purine nucleosides of RNA and DNA have the same specific activities with regard to both their purine and sugar portions, it is inferred that the conversion of a ribonucleosyl to a deoxyribonucleosyl intermediate is the principal mechanism involved in this organism for the biogenesis of the purine nucleosides of DNA.