Five-prime cap of messenger RNA (5′ cap (or m^7G cap, for 7-methylguanosine cap))

The **five-prime cap** is a uniquely modified nucleotide structure at the 5′ end of eukaryotic mRNA, consisting most commonly of 7-methylguanosine (m^7G) attached via a 5′–5′ triphosphate linkage[1][3][4][7]. This cap plays a crucial role in the life cycle of mRNA, protecting against 5′ exonucleases, assisting in nuclear export, promoting translation initiation, and marking the transcript as “self” to the immune system[2][3][7]. The **degradation of messenger RNA** often begins with removal of the cap (decapping), followed by rapid enzymatic decay[5][2]. Variants of the cap structure include Cap-0 (base methylated guanosine), Cap-1 and Cap-2 (additional methylations on adjacent riboses)[1], and in some bacterial and eukaryotic cases can include NAD+ or other small molecule caps[1][2]. While not a therapeutic target itself, the enzymes that add or remove the cap—such as methyltransferases and decapping enzymes—play vital roles in gene regulation and can be relevant to disease processes[2][5].

Other names

Five-prime cap5′ capm7G cap7-methylguanylate capCap-0/Cap-1/Cap-2 (chemical variants)