試題詳解

1. Restriction endonucleases are commonly used in DNA cloning. Which of the following is not true?
(A) Restriction endonucleases are main components of the bacterial restriction- modification (R-M) system.
(B) The normal function of the R-M system is to degrade DNA from invading phages.
(C) In a R-M system, phosphatases are frequently used to protect the same DNA sequences of bacteria from digestion by the restriction endonucleases.
(D) The most useful R-M systems in DNA cloning are the type II system, and the restriction activities do not need ATP as a cofactor.
(E) In the type III R-M systems, one enzyme contains two different subunits, one for DNA recognition and modification, and another for DNA cleavage.