A new method fortherapid identification ofgenes encoding restriction andmodification enzymes

We haveconstructed derivatives ofEscherichia coil thatcanbe usedfortherapididentification of recombinant plasmids encodingDNA restriction enzymesandmethyltransferases. Theinduction ofthe DNA-damage inducible SOSresponse bytheMcrand Mrrsystems, inthepresence ofmethylated DNA,is usedtoselect plasmids encoding DNAmethyltransferases. Thestrains ofE.coli that wehaveconstructed aretemperature-sensitive fortheMcrandMrrsystems andhavebeenfurther modified toinclude alacZ gene fused tothedamage-inducible dinDlocus ofE.coil. The detection ofrecombinant plasmids encoding DNA methyltransferases andrestriction enzymesisasimple, onestepprocedure that isbasedontheinduction at therestrictive temperature ofthelacZgene. Transformants encoding DNAmethyltransferase genes aredetected onLBagarplates supplemented withXgalasbluecolonies. Usingthismethod, we have cloned avariety ofDNAmethyltransferase genesfrom diverse species suchas Neisseria, Haemophilus, Treponema,Pseudomonas,Xanthomonasand Saccharopolyspora.