Five prime untranslated region

The 5′ untranslated region (also known as 5′ UTR, leader sequence, transcript leader, or leader RNA) is the region of a messenger RNA (mRNA) that is directly upstream from the initiation codon. This region is important for the regulation of translation of a transcript by differing mechanisms in viruses, prokaryotes and eukaryotes. Despite its name, the 5′ UTR, or a portion of it is sometimes translated into a protein product. This product may involve in regulation of transcription, and translation of the main coding sequence of the mRNA, such as the sex-lethal gene in Drosophila. Regulatory elements within 5′ UTRs have also been linked to mRNA export. In many organisms, however, the 5′ UTR is completely untranslated, instead forming a complex secondary structure to regulate translation.