RNA-dependent DNA polymerases.

Reverse transcriptases are derived from retroviruses which use them to make DNA copies of their RNA genomes. They are multifunctional enzymes, but they are mainly used as RNA-directed DNA polymerases. Specifically, deoxyoligonucleotides (either oligo(dT) polymers, a collection of random DNA sequences, or a specific sequence) are used as primers for extension on RNA (usually messenger RNA) templates. The DNA synthesized from the RNA template is referred to as complementary DNA (cDNA). This unit describes appropriate reaction conditions along with applications such as synthesizing cDNA for insertion into bacterial cloning vectors, filling in and labeling the 3'termini of DNA fragments with 5' protruding ends, and its use for DNA sequencing in place of Klenow fragment.