IMR Press / FBL / Volume 17 / Issue 3 / DOI: 10.2741/3975

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on as a courtesy and upon agreement with Frontiers in Bioscience.

Open Access Review
Mechanistic insights into type III restriction enzymes
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1 Center for Retrovirus Research, Ohio State University, Columbus, OH. USA
2 Department of Biochemistry, Indian Institute of Science, Bangalore, India
Academic Editor:Piero R. Bianco
Front. Biosci. (Landmark Ed) 2012, 17(3), 1094–1107;
Published: 1 January 2012
(This article belongs to the Special Issue DNA motor proteins - biochemical and biophysical studies)

Type III restriction-modification (R-M) enzymes need to interact with two separate unmethylated DNA sequences in indirectly repeated, head-to-head orientations for efficient cleavage to occur at a defined location next to only one of the two sites. However, cleavage of sites that are not in head-to-head orientation have been observed to occur under certain reaction conditions in vitro. ATP hydrolysis is required for the long-distance communication between the sites prior to cleavage. Type III R-M enzymes comprise two subunits, Res and Mod that form a homodimeric Mod2 and a heterotetrameric Res2Mod2 complex. The Mod subunit in M2 or R2M2 complex recognizes and methylates DNA while the Res subunit in R2M2 complex is responsible for ATP hydrolysis, DNA translocation and cleavage. A vast majority of biochemical studies on Type III R-M enzymes have been undertaken using two closely related enzymes, EcoP1I and EcoP15I. Divergent opinions about how the long-distance interaction between the recognition sites exist and at least three mechanistic models based on 1D- diffusion and/or 3D- DNA looping have been proposed.

Restriction-modification system
DNA translocation
ATP hydrolysis
DNA looping
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