In vivo specificity of EcoRI DNA methyltransferase

• Published in: Nucleic acids research 1992-11, Vol.20 (22), p.6091-6096
• Main Authors: Smith, Dean W., Crowder, Scott W., Reich, Norbert O.
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Cloning, Molecular; DNA - metabolism; Enzymes and enzyme inhibitors; Escherichia coli; Escherichia coli - enzymology; Fundamental and applied biological sciences. Psychology; Hydrolases; Kinetics; Methylation; Plasmids; Site-Specific DNA-Methyltransferase (Adenine-Specific) - metabolism; Substrate Specificity
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/20.22.6091

The EcoRI adenine DNA methyltransferase forms par of a bacterial restriction/modification system; thi methyltransferase modifies the second adenine withii the canonical site GAATTC, thereby preventing thi EcoRI endonuclease from cleaving this site. We shov that five noncanonical EcoRI sites (TAATTC, CAATTC GTATTC, GGATTC and GAGTTC) are not methylate in vivo under conditions when the canonical site ii methylated. Only when the methyltransferase ii overexpressed is partial in vivo methylation of the fivi sites detected. Our results suggest that thi methyltransferase does not protect host DNA agains potential endonuclease-mediated cleavage a noncanonical sites. Our related in vitro analysis of thi methyltransferase reveals a low level of sequence discrimination. We propose that the high in vivo specificity may be due to the active removal of methylated sequences by DNA repair enzymes (J Bacteriology (1987), 169 3243–3250).