Cellular localization of dihydrofolate reductase-thymidylate synthase in carrot cells

The intracellular distribution and localization of dihydrofolare reductase-tymidylate synthase of wild type suspension carrot cells was analysed using cytochemical and immunocytochemical techniques; in both resting and growing normal cells (E4) the activity appeared to be predominantly cytoplasmic. The pattern of localization of the enzyme was also analysed during the different phases of the cell cycle. To this end carrot cells were synchronized with aphidicolin (an inhibitor of the alpha-like DNA polymerase wich blocks cells at the G1/S boundary) and cycle phases checked by labelled-thymidine incorporation. Protoplasts obtained from cells inhibited with aphidicolin or from cells sampled at different times after the removal of the drug (S and G2 phase) failed to show a nuclear localization of DHFR-TS. These results indicate that the carrot bifunctional enzyme does not change compartment during the cell cycle