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Inverted terminal repeats permit the average length of amplified DNA fragments to be regulated during preparation of cDNA libraries by polymerase chain reaction.

A simple polymerase chain reaction (PCR)-based technique for construction of cDNA libraries starting with very small amounts of cells or tissues is described. The technique is based on the insertion of inverted terminal repeats into amplified cDNAs which permit short molecules to generate "pan"-type structures at each cycle of PCR amplification and thus to escape annealing with primers. This allows one to avoid amplification of primer dimers and makes it possible to perform oligonucleotide tailing of the first cDNA strands followed by PCR amplification in the same tube. Moreover, the average size of amplified cDNAs can be controlled by varying the primer concentration.