The modification of pre-messenger RNA (pre-mRNA) is essential for gene expression in eukaryotes. A pivotal event in this process, directly influencing the commencement of protein synthesis, involves the addition of a 5′ cap. This cap, a modified guanine nucleotide, is attached to the 5′ end of the pre-mRNA molecule. An example includes the addition of 7-methylguanosine (m7G) to the terminal phosphate of the pre-mRNA.
The presence of this cap structure is critical for several reasons. It protects the mRNA from degradation by exonucleases, enhancing its stability and lifespan. Furthermore, the cap serves as a recognition signal for ribosomes, the cellular machinery responsible for protein synthesis. Its presence facilitates the efficient binding of the mRNA to the ribosome, a prerequisite for the initiation of translation. Historically, the discovery of the 5′ cap unveiled a key regulatory mechanism influencing gene expression and provided insights into the complexities of mRNA processing.
