NUCLEOTIDE-METABOLISM AND NUCLEIC-ACID SYNTHESIS IN MOUSE THYMOCYTES

Nucleotide pool sizes, DNA polymerizing enzymes and DNA synthesis were studied in mouse thymocytes over 24 h of culture in Marbrook chambers. The initial rate of cell division was high with an average mitotic index of 1.6%/h for 12 h, followed, by a decline to 0.14% h at 24 h. The decline in DNA synthesis was not closely correlated with the activities of DNA-dependent DNA polymerases-.alpha. or -.beta. or with the activity of terminal deoxynucleotidyl transferase. The amounts of several ribo- and deoxyribonucleotides per thymocyte were measured using high performance liquid chromatography and DNA polymerase. Pool sizes of ATP, GTP, dATP and dTTP were less than 10% of pool sizes commonly observed in mammalian cells. The rates of DNA and RNA synthesis in thymocytes may be critically affected by minor changes in the availability of nucleotides. Cultures of thymocytes serve as useful experimental systems for investigation of nucleotide and nucleic acid metabolism during lymphoid differentiation.