試題詳解

3. The E. coli recombinant plasmid pBR322 has been widely utilized in genetic engineering experiments. pBR322 has all of the following features except:
(A) a number of conveniently located recognition sites for restriction enzymes.
(B) a number of palindromic sequences near the EcoRI site, which permit the plasmid to assume a conformation that protects newly inserted DNA from nuclease degradation.
(C) a replication origin, which permits it to replicate autonomously.
(D) resistance to two different antibiotics, which permits rapid screening for recombinant plasmids containing foreign DNA.
(E) small overall size, which facilitates entry of the plasmid into host cells.