Inhibition of unwinding and ATPase activities of pea MCM6 DNA helicase by actinomycin and nogalamycin.

Pea mini-chromosome maintenance 6 (MCM6) single subunit (93 kDa) forms homohexamer (560 kDa) and contains an ATP-dependent and replication fork stimulated 3' to 5' DNA unwinding activity along with intrinsic DNA-dependent ATPase and ATP-binding activities [Plant Mol. Biol. 2010; DOI: 10.1007/s11103-010-9675-7]. Here, we have determined the effect of various DNA-binding agents, such as actinomycin, nogalamycin, daunorubicin, doxorubicin, distamycin, camptothecin, cyclophosphamide, ellipticine, VP-16, novobiocin, netropsin, cisplatin, mitoxantrone and genistein on the DNA unwinding and ATPase activities of the pea MCM6 DNA helicase. The results show that actinomycin and nogalamycin inhibited the DNA helicase (apparent Ki values of 10 and 1 μM, respectively) and ATPase (apparent Ki values of 100 and 17 μM, respectively) activities. Although, daunorubicin and doxorubicin also inhibited the DNA helicase activity of pea MCM6, but with less efficiency; however, these could not inhibit the ATPase activity. These results suggest that the intercalation of the inhibitors into duplex DNA generates a complex that impedes translocation of MCM6, resulting in the inhibitions of the activities. This study could be useful in our better understanding of the mechanism of plant nuclear DNA helicase unwinding.