The mechanism of DNA methylation by the restriction endonuclease from E. coli K.
Restriction endonucleases are strain-specific enzymes which enable bacteria to recognize and destroy foreign DNA by making double-stranded scissions at a limited number of sites. These bacterial strains also possess DNA methylases which modify the DNA in order to protect it from the homologous restriction enzymes. These restriction endonucleases have been classified into three different types (Yuan, 1981). The Type I enzymes, such as the one coded by E. coli K, are multifunctional proteins composed of three different subunits. EcoK can catalyze three different reactions: DNA cleavage (which requires ATP and AdoMet), ATP hydrolysis (which is coupled to DNA cleavage) and DNA methylation (which requires AdoMet). We have made a detailed study of the reaction mechanism of EcoK in order to understand certain unusual features, such as its ability to catalyze two opposing reactions — restriction and modification — and the cleavage of DNA at sites distal from the original binding site.
KeywordsMajor Groove Allosteric Effector Methylase Activity Antirestriction Protein EcoK Restriction
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