text: The standard biochemistry and molecular biology textbooks describe non-coding nucleotides in mRNA located between the 5 end of the gene and the translation initiation codon. These regions are called 5-untranslated regions or 5-UTRs. Similar regions called 3-untranslated regions (3-UTRs) are found at the end of the gene. The 5-UTRs and 3UTRs are very short in bacteria but they can be several hundred nucleotides in length in eukaryotes. They contain short elements that control the initiation of translation (5-UTRs) and transcription termination (3'-UTRs) as well as regulatory elements that may control mRNA stability, processing, and targeting to different regions of the cell.