Gradient PCR Series landed introduce the principle of land PCR (Touchdown PCR) PCR knowledge Touchdown PCR reaction annealing temperature 1 ° C every cycle to reduce the annealing temperature until it reaches the "Touchdown", then this annealing temperature about 10 cycle. The method initially appear complex reaction is carried out in order to avoid to determine the optimal annealing temperature and the optimization process. Any differences between the correct and non-correct annealing temperature will result in each cycle twice the difference of the amount of PCR product (resulting in 4-fold difference) per degree Celsius. Therefore, the correct product can be obtained with respect to the non-correct products enriched in another application of the method in determining the DNA sequence of a known sequence peptide. The specific process is as follows: using two sets of known sequence peptide at both ends may be paired Jane primers, only need to know that the period length of the 13 amino acid peptide sequence, the 5 'and 3' primer of each length of 18 bases (6 amino acids) between the two intervals of one or more bases. Using degenerate primers that can be "Touchdown PCR. Obtained by this method will be a large number of the product, but because by the peptide sequence can know the exact distance between the primers, it is possible according to the size of the product to select the desired product. The advantage of this method is that correctly paired the product of primer and template can be enriched. If cloning and measuring PCR products will be a dozen can correctly determine the peptide coding sequence, the design of hybridizing oligonucleotides. The technique is particularly suitable for the polypeptide constituted by Ser, Lys, and Arg (each with six codons). Touchdown PCR advantages: Comprehensive relatively common gradient PCRhttp :/ / www.jntckj.cn/ technology and maximum tolerated dose of polymerase chain reaction, that the former procedure is simple, time-saving, the PCR amplification can be completed, but the disadvantage is the annealing temperature is not prone to false positives; although the maximum tolerated dose of polymerase chain reaction procedures are complicated, need instrument with a larger memory, but it can be very effective in reducing or avoiding false positives, and not in the ideal working conditions (such as the optimal magnesium ion concentration) can also be amplified product. This land is the advantage of PCR technology. But I think. Can be expanded by the conventional PCR technique out, try to use ordinary polymerase chain reaction, although the landing polymerase chain reaction save time and effort, but it is in a very wide annealing temperature amplification, mess bands certainly Doha . Although electrophoresis may not see. The touchdown PCR an advantage that can increase the specificity of certain genes, not only my own in the expansion of the difficult process of gene discovered the advantages, and also recommend to the people around you, if the conventional PCR cycling program of gene amplification effect poor, I came hot start plus landing PCR in the case of high non-specific background, this move is indeed effective, but not absolute.