PYRIMIDINE DEOXYRIBONUCLEOSIDES ARE PHOSPHORYLATED TO TRIPHOSPHATES AT LOW-TEMPERATURES TOO, BUT ARE NOT INCORPORATED INTO DNA OR PHOSPHOLIPIDS

Thymidine (Thd) was phosphorylated to dTTP also at 0 degrees C, both i n Ehrlich ascites tumor cells and human tonsillar lymphocytes, but was not incorporated into DNA. The uptake and phosphorylation of C-14-Thd into the pool showed regular kinetics (Km 6,6 uM), and the main metab olite was dTTP (75-84%) both at 0 degrees C, and 37 degrees C. Similar ly, deoxycytidine (dCyd) was also transported and phosphorylated to nu cleotides (76%) at low temperature, but no incorporation into DNA and phospholipid precursor liponucleotides could be detected at 0 degrees C Under the same conditions, at 37 degrees C, when lymphocytes were la beled with 5-H-3-dCyd, 51% of the total pool radioactivity was found i n liponucleotides. Transport and phosphorylation of deoxynucleosides s eem to be tightly coordinated at both temperatures, which processes ar e directly coupled to membrane-phospholipid and DNA biosynthesis, but only at physiological temperature while they seem ''uncoupled'' at low temperature. The fact that nucleoside phosphorylation occures also at low temperature has implications for several experimental techniques used in cell biology.