Complementary DNA (cDNA) is synthesized from single-stranded RNA, typically mRNA. cDNA is produced naturally by retroviruses, or it can be made synthetically using mature or fully spliced mRNA, and reverse transcriptase. Through pairing RNA bases with their DNA counterparts, reverse transcriptase generates intron-free cDNA.
cDNA encoding a particular protein can be transferred into a recipient cell where the protein is not naturally produced, resulting in protein production. Since cDNA does not have introns, it can be expressed in prokaryotic cells which lack intron-removing enzymes, leading to the production of specific proteins of interest. cDNA can also be used for gene probing, for creating a cDNA library, and for gaining an insight into the gene coding for the original template mRNA.