Structure-Function Differences Among Type I Restriction Endonuclease

Burckhard's Model for the Effect of SAM on the Structure of EcoKI

Burckhardt et al., (1981) J. Mol. Biol. 153, 425-440.

"The SAM binding to the M subunits would lead to a conformational change in the enzyme. The M subunits would use the methyl group of the SAM as a probe for the presence of methylated bases in the major groove. In the case of modified DNA (both strands methylated), the two M subunits would be prevented from going into the major groove because of steric hindrance from the two methylated adenines.......In the case of heteroduplex DNA (one strand methylated), one M subunit would remain outside the major groove at one domain because of the methylated base,.......Methylation would occur after interaction with ATP.

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