RESTRICTIN ENDONUCLEASE

Endonuclease are enzymes that produce internal cuts, called cleavage, in DNA molecules. Many endonucleases cleave DNA molecules at random sites. But a class of endonucleases cleaves DNA only within or near those sites which have specific base sequences, such endonucleases are known a restrictin endonucleases, and the sites recognised by them are called recognition sequences and the recognition sequences are different and specific for the different restriction endonucleases of restriction enzymes. Restiction enzymes were discovered due to and named after the phenomenon of host restriction of bacterial phages. When a phase DNA released from one bacterial stain (Say E. coli strain such a phage is designated is used to infect another strain (say E. coli strain K ) the effieicney of phage growth on the latter (strain K) is only a very small fraction of the efficiency on the former strain C some phages that survive grow normally on the second strain, and are now referred to as K these phage particles infect strain K with the same efficiency restrict the growth of the phage to teh strain concerned. This restriction on phage host range is due to the presence of restrtiction enzyme.