[21] Specific synthesis of DNA in vitro via a polymerase-catalyzed chain reaction

This chapter discusses the specific synthesis of deoxyribonucleic acid (DNA) in vitro through the medium of a polymerase-catalyzed chain reaction. A method whereby a nucleic acid sequence can be exponentially amplified in vitro is described in the chapter. The same method can be used to alter the amplified sequence or to append new sequence information to it. It is necessary that the ends of the sequence be known in sufficient detail that oligonucleotides can be synthesized, which will hybridize to them and that a small amount of the sequence be available to initiate the reaction. The oligonucleotides are complementary to different strands of the desired sequence and at relative positions along the sequence such that the DNA polymerase extension product of the one, when denatured, can serve as a template for the other and vice versa. Oligonucleotides were synthesized using an automated DNA synthesis machine (Biosearch, Inc., San Rafael, California) using phosphoramidite chemistry. “Mispriming"” can be usefully employed to make intentional in vitro mutations or to add sequence information to one or both ends of a given sequence. The chapter explores the possibility of utilizing a heat-stable DNA polymerase so as to avoid the need for addition of new enzyme after each cycle of thermal denaturation