Let’s say that you want to insert a DNA sequence into a bacterium and NOT have the bacterium cut up the DNA. However, for some reason, every time you add it in, the DNA is cut and your experiment is ruined. With which of the following enzymes can you treat your DNA sample prior to transforming it into the bacterium to prevent this problem from occurring?

a) kinases

b) phosphatases

c) ligases

d) methylases

e) exonucleases


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The correct answer is D. The whole point is that bacteria tend to cut up extraneous amounts of DNA that that they take in because it could be dangerous to the bacterium. The enzymes that cut up the DNA are usually called restriction enzyme that cut at particular sequences of nucleotides. In this case, the reason why bacterial DNA is protected from the restriction enzymes is because the DNA is methylated and the methylation serves as an indicator to the bacterial enzymes that the DNA is not intended to be destroyed. Thus, if you added DNA to the sample that had methylase then it would get methylated and when it got added to bacterial cells, the bacterium would be tricked into thinking that the DNA belongs to itself and it would not cut it up. 

For that reason, the answer is D – methylases.