UTR

Untranslated regions (UTRs) are portions of a messenger RNA (mRNA) that are not translated into a protein. They lie at the ends of the coding sequence: the 5' UTR precedes the start codon, and the 3' UTR follows the stop codon. Although they do not code for amino acids, UTRs play essential roles in regulating gene expression after transcription.

UTRs influence several aspects of mRNA biology, including translation initiation, stability, localization, and turnover. The 5' UTR can affect ribosome recruitment and scanning, and it may contain regulatory features such as upstream open reading frames (uORFs) or secondary structures that modulate translation. The 3' UTR often harbors binding sites for RNA-binding proteins and microRNAs, motifs that determine mRNA half-life, localization within the cell, and translational efficiency. It may also contain polyadenylation signals and localization elements that contribute to post-transcriptional regulation.

Regulatory elements within UTRs are a major area of study because changes in these regions can alter gene expression without altering the protein sequence. Mutations or polymorphisms in UTRs have been associated with disease susceptibility, development, and differences in drug response. Experimental approaches, including reporter assays, RNA-binding protein mapping, and microRNA interaction studies, are used to elucidate UTR function. Comparative genomic analyses show that many UTRs are conserved across species, reflecting functional constraints on post-transcriptional regulation.

Note: In biology, UTR most commonly refers to untranslated regions of mRNA, but the acronym can have other meanings in different fields. This article focuses on the genetic context and regulatory roles of UTRs.