Purine and pyrimidine content of the nucleic acids of nuclei and cytoplasm.

The nuclei of mammalian liver cells have been shown to contain, in addition to desoxypentose nucleic acid (DNA), a pentose nucleic acid (PNA) which is functionally different from the PNA of the cytoplasm (1). In the investigations to be described here the proport,ions of purine and pyrimidine in these two types of PNA in calf liver, kidney, thymus, and heart have been found to be strikingly different from each other and to differ also from the base ratios of DNA. This evidence of structural difference supports the previous finding of metabolic differences in these nucleic acids. The data presented also have a significant bearing on the problem of cell differentiation by showing that, although one nucleic acid of the nucleus (DNA) may remain unchanged in composition in the course of embryologicaldevelopment, another (PNA) shows marked variation. Since the nucleic acids also appear to be related to genie structure and function, the data also are of significance in this connection.