Primer extension

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Please improve this article if you can. (December 2007)

Primer extension is a technique whereby the 5' ends of RNA or DNA can be mapped.

Primer extension can be used to determine the start site of RNA transcription for a known gene. This technique requires a radiolabelled primer (usually 20 - 50 nucleotides in length) which is complementary to a region near the 5' end of the gene. The primer is allowed to anneal to the RNA and reverse transcriptase is used to synthesize complementary cDNA to the RNA until it reaches the 5' end of the RNA. By running the product on a polyacrylamide gel, it is possible to determine the transcriptional start site, as the length of the sequence on the gel represents the distance from the start site to the radiolabelled primer.