Restriction-modification system types

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. 

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... 

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,... 

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

Restriction. The bacterial restriction modification system consists of DNA restriction endonuclease (Pingoud, 2004) and a matched modification enzyme (methylase, i.e. methyltransferase). The restriction endonucleases recognize specific sequences within dsDNA on which the hydrolysis takes place. Three types of restriction enzymes (Table 13.4) have been identified (Yuan, 1981). 

Two types of restriction-modification system have been found in bacteria. In type I systems, the methy-lase and R. e. are both associated with a complex containing three different polypeptide chains an a-chain with R.e activity, a P-chain with methylase activity and a y-chain with the recognition site for the DNA sequence. Type I systems require S-adenosyl-t-me-thionine and ATP for both R.e. and methylase activities they are less specific, and cleavage sites may be random and far removed (1,000 base pairs) from the 5 side of the recognition site. In type II systems, me-thylases and R.e. are separate, 5-adenosyl-L-methio-... 

Wilson, G. G. 1988. Type 11 restriction- modification systems. Trends Genet, 4 314-8. 

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. 

Smirnova et al. demonstrated the determination of the insecticide, carbaryl, using a two-chip system. The first chip (for the hydrolysis of carbaryl) had a simple Y-shaped channel while the second chip (for the diazo couphng reaction between hydrolyzed products and 2,4,6-trimethylaniline)—the extraction required special channel shapes with a partial surface— modification obtained by using capillary-restricted modification (CARM) (Figure 35.11). " Determination of carbaryl pesticide in water with sufficient sensitivity was carried out with an analysis time of 8 min. In a similar manner, Honda et al. developed a combination of a tube-type enzyme-immobilized microreactor and a microextractor with partial surface modification to produce optically pure amino acids. 

Catalytic Properties. In zeoHtes, catalysis takes place preferentially within the intracrystaUine voids. Catalytic reactions are affected by aperture size and type of channel system, through which reactants and products must diffuse. Modification techniques include ion exchange, variation of Si/A1 ratio, hydrothermal dealumination or stabilization, which produces Lewis acidity, introduction of acidic groups such as bridging Si(OH)Al, which impart Briimsted acidity, and introducing dispersed metal phases such as noble metals. In addition, the zeoHte framework stmcture determines shape-selective effects. Several types have been demonstrated including reactant selectivity, product selectivity, and restricted transition-state selectivity (28). Nonshape-selective surface activity is observed on very small crystals, and it may be desirable to poison these sites selectively, eg, with bulky heterocycHc compounds unable to penetrate the channel apertures, or by surface sdation. 

The effect of the incorporation of a succinimide (21) moiety into a peptide chain (another type of Cj -o- Nj. ring restriction) has been examined carefully (60, 61). The five-membered succinimide annular system is an intermediate in the repair of selective degradations of side-chain deamidated proteins. It has been shown both theoretically and experimentally that L-Asu-Xxx- (Asu, a-aminosuccinyl) dipeptide sequences strongly favor the type-lT fS-tum, a behavior similar to that of the y-lactam modification discussed above. 

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