BCH5425 Molecular Biology and Biotechnology Dr. Michael Blaber
The restriction/modification system in bacteria is a small-scale
immune system for protection from infection by foreign DNA. W.
Arber and S. Linn (1969) Plating efficiencies of bacteriophage
lambda (l phage) grown on E. coli strains C, K-12 and B, when
plated on these bacteria: |E. coli strain on which parental
phage had been grown| Thus, this combination of a specific
methylase and endonuclease functioned as a type of immune system
for individual bacterial strains, protecting them from infection
by foreign DNA (e.g. viruses). Such endonucleases are referred
to as "restriction endonucleases" because they restrict the DNA
within the cell to being "self". The combination of restriction
endonuclease and methylase is termed the "restriction-
modification" system. Of course, this type of protective system
is beaten if the attacking phage was previously grown on the
same strain as that which it is infecting. In this case the
phage will have its DNA alrea