In E Coli, the Adenine in the Sequence GATC Is Methylated

question 2

Multiple Choice

In E. coli, the adenine in the sequence GATC is methylated by the Dam enzyme. In the same cells, a restriction endonuclease recognizes and cleaves dsDNA with the sequence GATC on either strand. Why does E. coli have these two enzymes?

• A) The enzymes cut the E. coli genome into pieces that bind to viral particles and inhibit viral replication.
• B) The enzymes increase the rate of mutation and genome rearrangement, thus increasing the likelihood that E. coli cells will mutate and become resistant to viral infection.
• C) The enzymes encourage lysogeny because the cleavage sites are recognized by viral integrases.
• D) The enzymes protect E. coli from infection by preferentially degrading viral or other exogenous DNA that is not methylated.

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