Structure-Function Differences Among Type I Restriction Endonuclease

Type I Restriction and Modification

GENE           FUNCTION             MUTATIONS

hsdR           Restriction          Res- Mod +

hsdM           Methylation          Res- Mod-

hsdS           DNA Specificity      Res- Mod-

Endonuclease - requires all 3 gene products + ATP + SAM (S-adenosyl methionine) + Mg²⁺

Modification requires only HsdM and HsdS + SAM

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