A 5'-MONOPHOSPHATE FORM OF BREDININ SELECTIVELY INHIBITS THE ACTIVITIES OF MAMMALIAN DNA-POLYMERASES IN-VITRO

Bredinin is an immunosuppressive drug which is used clinically in Japa n. In this study, we investigated bredinin's molecular mode of action to clarify its immunosuppressive effects. We focused on the DNA polyme rases in the somatic DNA synthesis which may be required in the proces s of lymphocyte differentiation. We found that bredinin-5'-monophospha te (breMP) could be a potent inhibitor of mammalian DNA polymerase alp ha (pol. alpha) and beta (pol. beta) in vitro, although bredinin itsel f has no such effects. BreMP inhibited the pol. alpha activity at less than 7 mu g/ml and the pol. beta activity at 7 mu g/ml. Neither breMP nor bredinin influenced the activities of a plant DNA polymerase, pro karyotic DNA polymerases such as E. coli DNA polymerase I and Tag DNA polymerase, or DNA-metabolic enzymes such as DNase I, indicating that breMP selectively suppressed the activities of the mammalian DNA polym erases. For pol. beta, breMP acted by competing with both the substrat e and template-primer. For pol. alpha, it acted by competing only with the substrate, and non-competitively with the template-primer. The ri bose of bredinin is quickly and quantitatively converted to its ribose -5'-phosphate form in vivo as soon as it is incorporated into cells. T he action mode of bredinin and its use as an immunosuppressive drugs a re discussed based on these results.