modification and restriction system
modification and restriction systema system, generally involving the action of METHYLASES and RESTRICTION ENZYMES, that is thought to protect microbial CELLS from invading foreign DNA, such as PLASMID DNA or BACTERIOPHAGE DNA. The restriction enzyme cleaves the incoming DNA, at or near specific sites, and it is degraded. The same sites on the DNA of the host cell are protected from cleavage by modification of BASES at those sites, generally by METHYLATION.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005