Intercistronic

Intercistronic is an adjective describing anything situated between cistrons, the functional units of gene expression as defined by genetic mapping. In biology, it most often refers to the region between coding sequences within a polycistronic transcription unit, such as bacterial operons or organellar genomes. The intercistronic region is the spacer separating adjacent genes in a single transcript.

In bacteria, polycistronic mRNA encodes several proteins; translation of downstream genes depends partly on the intercistronic sequence. This region may contain regulatory elements such as ribosome-binding sites (RBS) or translation initiation signals for downstream cistrons, and the physical distance between stop codon and start codon can influence translational coupling and reinitiation efficiency. The region may also house transcriptional terminators or antisense elements that affect processing, though its primary role is in translation.

In mitochondrial and chloroplast genomes, intercistronic spacers separate coding regions within polycistronic transcripts and can be subject to RNA processing to release mature RNAs.

In genetic engineering, intercistronic sequences are used to arrange multiple genes in a single construct; commonly included spacers or linkers, promoter and RBS choices, sometimes using strategies like internal ribosome entry sites (IRES) or self-cleaving 2A peptides to enable the expression of multiple proteins from a single transcript.

The term is specialized and most often encountered in prokaryotic and organellar genetics; usage can vary and intercistronic spacer is a common alternative designation in modern literature.