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