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#cistron

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Transcription Basics

A cistron codes for

Cistron defined by cis-trans complementation test represents genetic element encoding single complete polypeptide chain. In polycistronic bacterial messenger RNAs, each cistron owns independent Shine-Dalgarno ribosome binding site, start codon, and stop codon enabling separate translation initiation producing distinct protein products from same transcript. Structural analysis shows cistron may correspond to protein domain or entire subunit of larger complex. Though often synonymous with gene in simple organisms, cistron terminology clarifies operon organization where one operon contains multiple cistrons. Therefore coding one polypeptide chain operational definition holds across prokaryotes and eukaryotes.

Ref: Jacob and Monod 1961 J Mol Biol Cis-trans test cistron concept; Lodish Chapter 8 Cistron encodes polypeptide

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Transcription Basics

Translation unit is also called

Translation unit conceptually frames messenger RNA segments decoded by ribosome, including 5' leader, open reading frame specifying amino acid chain from start codon AUG to stop codon, and 3' trailer. Open reading frame designation emphasizes continuous triplet codons without interruption that could encode protein when translated. Many transcripts contain upstream ORFs regulating main ORF via translational repression, while main ORF produces functional product. Bioinformatics prediction annotates longest ORF as candidate coding sequence. While replicon defines replication and cistron defines genetic complementation, ORF explicitly denotes nucleotide interval translatable.

Ref: NCBI Bookshelf ORF translation unit definition; Watson Chapter 15 Open reading frames mapping

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