The functional structure of mRNA in both prokaryotes and eukaryotes is orderly arranged as follows: 5′ non-coding region (5′ untranslated region), coding region, and 3′ non-coding region (3′ untranslated region) (Fig. 9-3). The translation initiation codon AUG is present at the start of the coding region. A sequence complementary to 16S rRNA is present in the 5′ non-coding region in eubacteria. This is the sequence to which ribosomes bind. No such sequence exists in eukaryotes; instead, they contain proteins that bind to the 5′ terminal cap structure to facilitate accurate binding between mRNA and ribosomes. The 3′ non-coding region in eukaryotic mRNA contains a sequence related to the mRNA degradation rate. The coding region between these two regions encodes the amino acid sequence of a protein.