THE BIOCHEMICAL-INHIBITION MODE OF BREDININ-5'-MONOPHOSPHATE ON DNA-POLYMERASE-BETA

We reported previously [T. Horie, Y. Mizushina, M. Takemura, F. Sugawa ra, A. Matsukage, S. Yoshida, K. Sakagucki, Int. J. Mel. Med., 1 (1998 ) 83-90.] that a 5'-monophosphate form (breMP) of bredinin, which has been used clinically as an immunosuppressive drug, selectively suppres sed the activities of mammalian DNA polymerase alpha (pol. alpha) and beta (pol. beta). In a preliminary study of the action mode, for pol. beta, breMP acted by competing with, unexpectedly, not only the substr ate but also with the template-primer. The mode might be attributable to the structure and function of pol. beta itself. We therefore invest igated the biochemical inhibition mode of pol. beta in more detail by using two pol. beta fragments which were proteolytically separated int o the template-primer-binding domain and the catalytic domain. BreMP i nhibited only the catalytic activity of the catalytic domain fragment, and could not bind to the template-primer-binding domain fragment, su ggesting that it directly competes with the substrate at its binding s ite of the catalytic domain, and indirectly, but simultaneously and co mpetitively disturbs the template-primer incorporation into the templa te-primer-binding domain. (C) 1998 Elsevier Science B.V. All rights re served.