CYTOSINE DNA METHYLTRANSFERASE FROM WHEAT SEEDLINGS

A cytosine DNA methyltransferase has been isolated from wheat seedling nuclei and purified by chromatography on DEAE-cellulose, heparin-Seph arose, and Mono-Q FPLC. The specific activity of the enzyme was 236 un its/mg protein; its molecular mass by SDS-PAGE was 85-kD. The enzyme c atalyzes in vitro DNA methylation for a relatively long period, but it is very unstable in solution in the absence of substrates. The appare nt K-m value for S-adenosylmethionine is 6 mu M. The enzyme is active over a wide pH range (5.5-8.5), it is inhibited by NaCl and by the rea ction product S-adenosylhomocysteine with [I](50) values of 0.2 M and 12 mu M, respectively. The enzyme catalyzes both de novo and maintenan ce DNA methylation and displays a high rate of de novo methylation. Th e wheat seedling enzyme is similar to known plant cytosine DNA methylt ransferases.