DNA-BINDING AND METHYL TRANSFER CATALYZED BY MOUSE DNA METHYLTRANSFERASE

By using a purified fraction of mouse DNA methyltransferase we have sh own, by gel-retardation analysis, that the enzyme forms a low-affinity complex preferentially with hemimethylated DNA; the complexes formed with unmethylated or with fully methylated DNA are of even lower affin ity, and only very weak interaction occurs with DNA lacking CG dinucle otides. Interaction is inhibited by N-ethylmaleimide. Methyl transfer from S-adenosylmethionine is associated with the release of the fully methylated product from the complex. Complexes formed with the intact enzyme are extremely large, but limited trypsin treatment allows a maj or complex to enter the gel. DNA binding is not inhibited by this limi ted proteolysis of the native enzyme.