Transcriptases

Transcriptases are enzymes that synthesize a nucleic acid strand using a nucleic acid template. The term is used most often for reverse transcriptases, which synthesize complementary DNA (cDNA) from an RNA template, but it also describes RNA-dependent RNA polymerases that copy RNA templates in RNA viruses. In addition, some cellular enzymes with reverse-transcriptase activity, such as telomerase, use an RNA template to extend chromosomal ends.

Reverse transcriptases are found in retroviruses (for example HIV), in some retrotransposons, and in laboratory tools used for molecular biology. They catalyze the synthesis of cDNA from RNA, typically requiring a primer and divalent cations such as magnesium or manganese. Many reverse transcriptases lack 3' to 5' exonuclease proofreading, which contributes to higher mutation rates in cDNA products. They enable techniques such as cDNA synthesis, reverse transcription–polymerase chain reaction (RT-PCR), and the creation of cDNA libraries for sequencing and expression analysis.

RNA-dependent RNA polymerases are viral enzymes that use RNA templates to produce new RNA genomes or transcripts. They are essential for replication of RNA viruses and often initiate RNA synthesis de novo or with a primer. RdRPs are generally error-prone, which influences viral evolution and pathogenesis, and they are frequent targets for antiviral drug development.

Telomerase is a specialized reverse transcriptase that uses an RNA component as a template to extend telomeres at chromosome ends. Its catalytic subunit, often paired with an RNA template, maintains telomere length in stem cells and germ cells, with dysregulation linked to aging and cancer.

Applications of transcriptases span research and medicine, including gene expression analysis, diagnostics, and therapeutics, notably antiretroviral strategies that inhibit reverse transcription.