in the year 1963, two enzymes responsible for restricting the growth of E.coli was isolated. how did the enzyme act to restrict the growth of the bacteriophage?

The enzyme which restrict the growth of the bacteriophage are known as restriction enzyme.  In Bacteria these restriction enzymes (restriction endonucleases) cleave double stranded DNA at specific points into fragments, which are then degraded further by endonucleases. This prevents infection by effectively destroying the foreign DNA introduced by an infectious agent (such as a bacteriophage). Basically the enzyme restricts the replication of bacteriophage by cutting phage DNA into small pieces. It was later found that there were two sets of enzymes, one a methylase and the other is "restriction nuclease" which cuts DNA that isn't methylated at the sites the bacteria expects. The restriction nuclease enzymes cut the viral DNA if it doesn't have the correct methylation pattern. So if the viral DNA has have the correct methylation pattern, then virus can infect and produce new viruses and if the viral DNA doesn't have the correct methylation pattern, the viral DNA is cut and therefore can't replicate and so new viruses can't be produced.

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