The RY13 strain of the bacteria E. coli makes the restriction enzyme EcoR I, which cuts...

The RY13 strain of the bacteria E. coli makes the restriction enzyme EcoR I, which cuts at the sequence GAATTC. this occurs thousands of time in a full chromosome. Why doesn’t the enzyme cut the chromosome into tiny bits, killing the bacterium?

Expert Solution

E.coli apart from encoding the restriction enzyme EcoRI which cuts the dsDNA by recognizing GAATTC recognition sequence also encodes enzyme DNA methylase which specifically methylate specific nucleotide of the recognition sequence present in bacterial chromosome.

One such example is EcoRI methylase which basically attaches a methyl group at N6 position of second adenine nitrogenous base of EcoRI recognition sequence that leads to its modification. Due to the methylation, now the restriction enzyme EcoRI will not be able to recognize its recognition sequence as a result, it will not able to cleave or digest the bacterial DNA while when foreign viral DNA enters the bacteria (host), those viral DNA sequences are not methylated as a result EcoRI enzyme will be able to digest the viral DNA.

Hence, this restriction-modification system of the bacteria prevents its own DNA getting digest and simultaneously uses restriction enzyme as its defense mechanism.

gladiator answered 3 months ago

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