206 Part II: Water, Enzymology, Biotechnology, and Protein Cross-linking
Figure 8.18.PCR oligonucleotide-directed mutagenesis. Two sets of primers are used for the amplification of the
double-stranded plasmid DNA. The primers are positioned as shown and only one contains the desired base
change. After the initial PCR step, the amplified PCR products are mixed together, denatured, and renatured to form,
along with the original amplified linear DNA, nicked circular plasmids containing the mutations. Upon transformation
into E.coli,the nicked plasmids are repaired by host cell enzymes, and the circular plasmids can be maintained.