試題詳解

10. Bacterial restriction and modification (RM) systems are important for performing DNA cloning. Please choose one     correct     answer for 4 different types of RM systems.
(A) In the type II system, restriction and modification are mediated by the same enzyme with two different subunits, one for recognition and modification, and another one for DNA cleavage.
(B) The type III system contains the methyltransferase and endonuclease that are encoded as two separate proteins and act independently.
(C) The type I system contains two different enzymes; both of them recognize the same target DNA sequence and either cleave or modify the recognition sequence.
(D) In the type II system, one enzyme contains several different subunits that are independently responsible for DNA recognition, cleavage or methylation.
(E) The restriction enzymes in the Type II system do not need cofactors such as ATP; therefore, they are commonly used for DNA digestion in DNA cloning experiments.