What are the common primers used in reverse transcription?

Primers are short DNA oligonucleotides that serve as starting points for synthesizing new strands by binding to complementary sequences on the DNA template. Reverse transcription primers are necessary for initiating reverse transcription. The three common primers used in reverse transcription include oligo (dT) primers, random primers, and gene-specific primers. The RNA template and the downstream applications determine the best primer to use in a reverse transcription process. 

Oligo (dT) primers 

Oligo (dT) primers consist of a stretch of 12–18 deoxythymidines. They are the preferred choice of primer for obtaining full length copies of mRNA, constructing cDNA libraries from eukaryotic mRNAs, and 3’ rapid amplification of cDNA ends.

Random primers

Random primers are oligonucleotides with random base sequences that allow them to potentially anneal to any RNA species in the sample. They are commonly used for reverse transcription of small RNAs, prokaryotic mRNA, RNA with known secondary structures, noncoding RNAs, degraded RNA, and RNAs without poly (A) tails. 

Random primers can be used to transcribe 5’ ends of long genes but are not suitable for full-length reverse transcription of long RNA.

Gene-specific primers

Gene-specific primers, also known as sequence-specific primers, are designed based on known sequences of the target RNA and offer the most specific priming in reverse transcription. These primers greatly enhance the specificity and sensitivity of the RT-PCR and are the only type of primer that can be used for one-step RT-PCR applications.