[Isolation and properties of DNA-cytosine methyltransferase from Escherichia coli C]

Abstract

The method of isolation and partial purification of DNA-cytosine-methyltransferase (DC-methylase) from E. coli C is described. The enzyme underwent approximately 100-fold purification. The obtained preparation of DC-methylase can be additionally considerably purified by sedimentation in sucrose gradient. Native molecular weight of DC-methylase from E. coli C. is 70,000. The activity of enzyme does not depend on the Mg2+ ions. DC-methylase E. coli C provides DNA of lambda phage in vitro with full resistance against restriction endonuclease EcoRII. In DNA methylated by DC-methylase the modified cytosine, mainly in C-MC and C-MC-T sequences, corresponds to the pyrimidine sequences of specific site EcoRII. DNA of lambda.B phage contains approximately 80 sites for modification by DC-methylase E. coli C. The results obtained point to the same specificity in vitro of DNA-cytosine-methylase E. coli C and DNA-methylase EcoRII.