Restriction-modification

Restriction/modification Degradation of DNA Chromosome-associated proteins Other... 

Burrus, V., C. Bontemps, B. Decaris, and G. Guedon. 2001. Characterization of a novel type II restriction-modification system, Sth368I, encoded by the integrative element ICEStl of Streptococcus thermophilus CNRZ368. Appl Environ Microbiol 67(4) 1522-8. 

These enzymes are isolated from bacteria, their natural source. There are many different restriction endonucleases isolated from a variety of bacteria that are now readily available commercially. In bacteria they act as part of a restriction/modification system that protects the bacteria from infection by DNA viruses. 

Restriction enzymes are another lifesaving mechanism that bacteria have evolved for their survival. Restriction enzymes can be considered a part of a bacterium s immune system, a system that is called its restriction-modification (or RM) system. This system was first discovered and explained by the Swiss microbiologist Werner Arber in 1968. 

Kitamori s group has proposed selective chemical surface modification utilizing capillarity (called the capillarity restricted modification or CARM method) (Hibara et al., 2005). In the CARM method, a microchannel structure combining shallow and deep microchannels and the principle of capillarity are utilized. The procedures are shown in Figure 19. A portion of an ODS/toluene solution (lwt%) is dropped onto the inlet hole of the shallow channel, and the solution is spontaneously drawn into this channel by capillary action. The solution is stopped at the boundary between the shallow and deep channels by the balance between the solid-liquid and gas-liquid interfacial energies. Therefore, the solution does not enter the deep channel. It remains at the boundary for several minutes and is then pushed from the deep channel side by air pressure. 

Type II restriction-modification systems differ from their type I and type III counterparts in that the endonuclease and DNA methylase activities are conducted by two separate enzymes (not a single multisubunit complex). The restriction endonuclease cleaves both strands of the DNA duplex within a defined recognition sequence, while the companion DNA methylase methylates a specific base within the same recognition sequence. In contrast... 

Figure V-15 The DNA methylase component of the restriction modification system methylates a specific cytosine or adenine residue, making it incapable of being acted on by the companion restriction endonuclease.

Fig. 13.1. Biological function of restriction/modification systems RM systems recognize and act on short palindromic DNA sequences. While the host genome is protected by the methyltransferase activity of the system, invading phage DNA is cleaved by the endonuclease activity.

A. Jeltsch and A. Pingoud. 1996. Horizontal gene transfer contributes to the wide distribution and evolution of type II restriction-modification systems J. Mol. Evol. 42 91-96. (PubMed)... 

Type I DNA restriction/modification systems have been found in many strains of Escherichia coli and Salmonella enterica (Bickle Kruger,... 

Restriction-modification system. A pair of enzymes found in most bacteria (but not eukaryotic cells). The restriction enzyme recognizes a certain sequence in duplex DNA and makes one cut in each unmodified DNA strand at or near the recognition sequence. The modification enzyme methylates (or modifies) the same sequence, thus protecting it from the action of the restriction enzyme. 

Horizontal gene transfer may be a common event. For example, genes that inactivate antibiotics arc often transferred, leading to the transmission of antibiotic resistance from one species to another. For restriction-modification systems, protection against viral infections may have favored horizontal gene transfer. 

At present, three different types of restriction-modification systems are known-types I, II, and III. 

Restriction-modification is a term for bacterial enzyme systems that cleave DNA sequences. Each system consists of two distinct enzyme activities a DNA methylase and an endonuclease that catalyzes the double-strand DNA break. Type I restriction endonuclease systems have both methylase and nuclease activities in one protein molecule, which contains three subunits. One subunit contains the nuclease, one the methylase, and one a sequence recognition determinant. The recognition site is not symmetrical, and cleavage occurs some distance (up to 10 kbp) away from the recognition site, although methylation occurs within the recognition site. 

See also DNA Methylation, Restriction-Modification, Restriction Enzyme Types... 

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