transcriptase

Transcriptase is an enzyme that synthesizes a nucleic acid strand using a nucleic acid template. The term is used for enzymes that copy DNA into RNA (DNA-dependent RNA polymerases) and those that copy RNA into DNA (RNA-dependent DNA polymerases, commonly called reverse transcriptases). In cellular biology, transcription is carried out by DNA-dependent RNA polymerases to produce RNA transcripts from a DNA template; in contrast, reverse transcription uses RNA as a template to make DNA.

RNA-dependent DNA polymerases, or reverse transcriptases, are found in retroviruses and in certain cellular elements such as telomerase and some transposons. They synthesize DNA from an RNA template and often degrade the RNA strand of RNA-DNA hybrids as part of the process. Retroviral reverse transcriptases are essential for converting viral RNA into DNA, enabling integration into the host genome.

In molecular biology laboratories, reverse transcriptases are widely used to convert RNA into complementary DNA (cDNA), a step required for techniques such as RT-PCR, quantitative RT-PCR, and cDNA library construction. Enzymes used for this purpose are derived from retroviruses or engineered variants with improved properties, including higher thermostability.

Telomerase is a specialized reverse transcriptase that carries its own RNA template and synthesizes DNA repeats to extend chromosome ends (telomeres) in many eukaryotes, thereby contributing to genome stability and cellular aging.

See also: RNA polymerase, reverse transcriptase, telomerase.