Primer extension

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

In this technique, we need an oligonucleotide from a transcribed DNA sequence. This oligonucleotide is annealed to the mRNA. The oligonucleotide sequence is used as a primer for the reverse transcriptase. Reverse transcriptase synthesizes one half of cDNA complementary to the mRNA till the 5' end of mRNA. We can then know the length of the new synthetised cDNA from the oligonucleotide sequence to the transcription start point.