DNA TOPOISOMERASE-I FROM RICE - ENZYME-SYNTHESIS IN GERMINATION, AND PARTIAL-PURIFICATION FROM CULTURED-CELLS

DNA topoisomerase I activity was observed in two-day-old seeds of rice when the seeds started germination at 30-degrees. Partially purified enzyme from cultured rice cells showed maximum activity at pH 7.0 with 75 mM NaCl in the absence of ATP, and showed resistance to camptothecin and DNA-intercalating reagents. The M(r) was ca 80 000 using gel permeation on a Sephacryl S-200 column. After fractionation of the homogenate from cultured rice cells by centrifugation, the activity was observed mainly in the crude nuclear fraction.