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RNA transcription is the template-directed enzymatic synthesis of an RNA molecule from a defined DNA sequence. It is catalyzed by RNA polymerase, which locally separates the DNA strands, reads the template strand in the 3′→5′ direction, and polymerizes complementary ribonucleoside triphosphates into an RNA chain in the 5′→3′ direction through phosphodiester-bond formation ^[1][2]. The resulting transcript has a nucleotide sequence complementary to the DNA template and corresponds, apart from uracil replacing thymine, to the coding-strand sequence.

The process comprises ordered stages of promoter recognition and initiation, promoter escape, elongation of the nascent RNA, and termination with release of the RNA product and polymerase from the transcription unit ^[2][3]. Its molecular components include a DNA template containing regulatory and transcribed regions, RNA polymerase, ribonucleoside triphosphate substrates, divalent metal ions in the catalytic center, and accessory factors that direct polymerase recruitment, start-site selection, processivity, pausing, RNA processing, and termination ^[2][3][4]. In eukaryotes, RNA polymerases I, II, and III synthesize specialized RNA classes through associated transcription machineries, with RNA polymerase II producing precursor messenger RNAs and numerous regulatory non-coding RNAs ^[3][4].