Oligo dT 18 primer

Oligo (dT)18 are single stranded oligodeoxyribonucleotides containing only deoxythymine (dT) repeats. This 18-mer oligonucleotide just anneal to poly(A) tail that found at the 3´-end of most mRNA molecules. Oligo (dT)18 is designed  to be used as a primer for first-strand cDNA synthesis with a reverse transcriptase, where Reverse Transcriptase is starting the reaction from the poly-A-end of mRNA . this primer is frequently employed when cDNA is used for cloning, cDNA library construction and qPCR.