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. 2023 Dec 21;12(1):9. doi: 10.3390/vaccines12010009

Figure 3.

Figure 3

mRNA Structure. The 5’UTR (5’ untranslated region) cap refers to a modification at the beginning of a messenger RNA (mRNA) molecule. This modification, known as the 5’ cap, plays a crucial role in gene expression and translation. It is added to the 5’ end of the mRNA molecule during transcription to protect the mRNA from degradation, protect the mRNA from exonuclease, and facilitate the initiation of translation. It consists of a modified nucleotide called 7-methylguanosine (m7G) attached to the 5’ end of the mRNA through a unique 5’-5’ triphosphate linkage. This structure is often referred to as “m7G cap”. The cap is essential for the initiation of protein synthesis (translation). It serves as a recognition site for the ribosome, the cellular machinery responsible for translating mRNA into proteins. Some regulatory proteins can interact with the cap structure to modulate gene expression. Here is a sequence of 5′UTR cap: GAGAATAAACTAGTATTCTTCTGGTCCCCACAGACTCAGAGAGAACCCGCCACCATGTTCGTGTTCCTGGTGCTGCTGCCTCTGGTGTCCA. The Kozak sequence guides the pre-initiation complex (PIC) and ribosome to the translation initiation point (start codon) and facilitates ribosome assembly to ensure accurate translation of the protein sequence. The widely accepted Kozak sequence consensus is GCCGCCACCATGG, with ATG as the start codon. The Open Reading Frame serves as the translation code. The 3′-UTR directly succeeds the translation termination codon. The genetic material contains sections with regulatory functions, which affect gene expression after transcription. These regions also have binding sites for regulatory proteins and microRNAs (miRNAs). Through binding to the specific areas within the 3′-UTR, miRNAs can reduce the production of different mRNAs by either blocking translation or directly leading to the destruction of the transcript. The 3′-UTR contains silencer sequences that interact with repressor proteins, thereby suppressing the production of the mRNA. Several 3’-UTRs also have AU-rich elements (AREs). Proteins attach to AREs to influence the stability or rate of degradation of transcripts in a specific area or to impact the commencement of translation. In addition, the 3’-UTR region of the mRNA transcript contains the AAUAAA sequence, which guides the attachment of many adenine residues, known as the poly(A) tail, to the mRNA’s end. Poly(A) binding protein (PABP) attaches to this tail, playing a role in controlling mRNA translation, stability, and export. For instance, when the poly(A) tail of the mRNA binds to the poly(A) binding protein (PABP), it interacts with proteins that are linked to the 5’ end of the transcript. This interaction leads to the formation of a circular structure in the mRNA, which enhances the translation process.