Cellular localization of Type I restriction-modification enzymes EcoKI, EcoAI, and EcoR124I-the most frequently studied representatives of IA, IB, and IC families-was analyzed by immunoblotting of subcellular fractions isolated from Escherichia coli strains harboring the corresponding hsd genes. EcoR124I shows characteristics similar to those of EcoKI. The complex enzymes are associated with the cytoplasmic membrane via DNA interaction as documented by the release of the Hsd subunits from the membrane into the soluble fraction following benzonase treatment. HsdR subunits of the membrane-bound enzymes EcoKI and EcoR124I are accessible, though to a different extent, at the external surface of cytoplasmic membrane as shown by trypsinization of intact spheroplasts. EcoAI strongly differs from EcoKI and EcoR124I, since neither benzonase nor trypsin affects its association with the cytoplasmic membrane. Possible reasons for such a different organization are discussed in relation of the control of the restriction-modification activities in vivo.

Institute of Microbiology Academy of Sciences of the Czech Republic Prague

References provided by Crossref.org

A residue of motif III positions the helicase domains of motor subunit HsdR in restriction-modification enzyme EcoR124I

The helical domain of the EcoR124I motor subunit participates in ATPase activity and dsDNA translocation

Interdomain communication in the endonuclease/motor subunit of type I restriction-modification enzyme EcoR124I

General and molecular microbiology and microbial genetics in the IM CAS

Characterization of a restriction modification system from the commensal Escherichia coli strain A0 34/86 (O83:K24:H31)