CELL-CYCLE REGULATION OF DEOXYCYTIDINE KINASE - EVIDENCE FOR POSTTRANSCRIPTIONAL CONTROL

Deoxycytidine kinase enzyme activity and deoxycitidine kinase mRNA con tent were determined at different positions of the cell cycle in perma nent cell lines. There was no variation of deoxycytidine kinase activi ty during the cell cycle in two cell lines, whereas in two other lines the enzyme activity was induced (10- and 15-fold) at the G1/S boundar y. In contrast, the level of deoxycytidine kinase mRNA never displayed any cell cycle-dependent changes. The decay of enzymatic activity was measured after addition of cycloheximide in different phases of the c ell cycle; the enzyme was much more stable in cells with constant acti vity. We suggest that post-transcriptional mechanisms account for the periodic behaviour of the enzyme activity, and that whether this regul ation can be detected depends on the half-life of deoxycytidine kinase .