Target selection, polymerase chain reaction

The polymerase chain reaction utilizes a thermostable DNA polymerase to amplify DNA through a series of temperature cycle steps. The key to the specificity of the reaction is the selection of oligonucleotide primers that hybridize to the opposite strands of the DNA being tested, about 400-2000 bp apart. If the sequence of the primers is unique within the genome, and the primers hybridize to the target DNA at a high enough temperature to avoid close matches (various... 

A number of methods are available for analyzing tumor HER-2 status. The selection of the method depends on the target molecule to be detected. The target molecules are DNA mRNA, and protein (Fig. 12.2). HER-2 gene amplification can be detected by Southern blot (Press et al., 1994), slot blot (Naber et al., 1990), and dot blot assays (Descotes et al 1993), fluorescence in situ hybridization (FISH) (Persons et al., 1997), in situ hybridization (ISH) on isolated nuclei or tissue sections (Smith et al., 1994), and polymerase chain reaction (Gramlich et al., 1994). Assays to determine mRNA oveiexpiession include Northern blot (Slamon et al., 1989), Western blot (Press et al., 1994), slot blot (Naber et al., 1990) and ISH (Naber et al., 1990). Methods to assess HER-2/mcm protein product overexpression... 

Figure 9.4. Request form for primer selection. The nucleotide sequence of a target DNA for polymerase chain reaction can be submitted for primer selection at Primer3 server.

The principle of in vitro selection is governed by a number of the same principles that apply to the Darwinian theory of evolution, as shown in Figure 2. First, the random sequence DNA is prepared by automated solid-phase synthesis. A mixture of four types of nucleotide is added in a stepwise condensation reaction process. When necessary, this DNA library may be converted to an RNA library by in vitro transcription or to a peptide library by in vitro translation. Second, the prepared DNA, RNA, or peptide library is subjected to affinity selection, and the molecules that bind to a target molecule are selected. Because only a very small part of the library is selected in each selection, the selected fraction is then amplified by a polymerase chain reaction (PCR) or a reverse transcription PCR (RT-PCR) technique. Successive selection and amplification cycles bring about an exponential increase in the abundance of the targeting DNA, RNA, or peptide until it dominates the population. 

---