The 5′UTR is the RNA sequence immediately upstream of the coding RNA. It is generally not translated, although some exceptions, in which part of the 5′ UTR is translated, do exist.18 In eukaryotes, its length ranges from a few nucleotides (nt) to several thousand, with an average in humans of about 200 nt.16 The 5′ UTR should possess a Kozak consensus sequence (ACCAUGG), which contains the translation initiation codon. It may also contain numerous regulatory elements, like CpG sites, uORFs, IRESs, and RBP binding sites, which will be treated later. Additionally, secondary structures, such as hairpin loops, may be important in translation regulation, and often occur within the 5′UTR. Thus, genetic variants modifying these regulatory elements can have important impact on the overall production of the protein by affecting RNA transcription, stability, and translation.16,19, 20
