Upstream of the start codon lies the 5' UTR, or untranslated region. The leader sequence is another name for it. It improves the efficiency of the translation process and is also necessary for compliance.
Prokaryotes and eukaryotes have different lengths and compositions of the 5' UTR region.
The ribosome binding sites are found in the prokaryotic 5' UTR, which is 3 to 10 nucleotides long. It has a unique sequence known as the Shine–Dalgarno sequence, which is AGGAGGU.
Eukaryotic 5' UTRs range in length from 100 to a few thousand nucleotides. It has the Kozak consensus sequence in it (ACCAUGG). Introns are hidden in the 5' UTR region of around 35% of genes.