Purification and properties of a novel DNA methyltransferase from cultured rice cells.

DNA methylttransferase activity has been observed in a total homogenate of rice cells grown in suspension culture using either native plant DNA or, under the conditions used, the more responsive hemimethylated poly (dI-MedC)*poly(dI-dC). Using the latter substrate we have purified an enzyme fraction 380-fold by salt extraction of chromatin, DEAE cellulose and phosphocellulose.
This purified fraction showed enzyme activity only, with poly
(d1-MedC)*poly(dI-dC) thus suggesting the occurrence in plants of a DNA methyltransferase specific for hemimethylated DNA. A Mr value of 54000 was calculated on the basis of the sedimentation coefficent which was determined by sucrose density gradient centrifugation. Apparent Km values for poly(d1- MedC)*poly(dI-dC) and S-adenosyl-L-methionin e were foundto be 17 µg/ml and 2.6 µM, respectively.