5'-Capping - guanosine-based caps
Many eukaryotic and viral mRNAs are modified at their 5' ends by addition of 7-Methylguanosine (N7-methyl guanosine or m7G), known as "Cap". "Capping" of the mRNA structure plays a crucial role in a variety of cellular processes which include translation initiation[1], splicing[2], intracellular transport[3] and turnover[4]. Capped mRNAs are generally more efficiently translated in wheat germ and reticulocyte in vitro translation systems[5], and they are less susceptible to exonuclease degradation during microinjection experiments compared to uncapped mRNAs[6]. They are enzymatically incorporated at the RNA 5'-end by bacteriophage T7 RNA Polymerase-mediated in vitro Transcription.
Figure 1 Structural features of guanosine-based di- & trinucleotide RNA cap analogs.
A guanosine derivative (N1) is linked via a 5',5'-triphosphate bridge to one (N2) or two ribonucleotides (N2pN3).
Table 1: Available guanosine-based di- & trinucleotide RNA cap analogs.
Contact us if you are interested in a cap analog not listed.
| N2 / N3 | Guanosine Cap structure (N1) | Cap type | |||
|---|---|---|---|---|---|
| G | m7G | m27,3'-OG | m32,2,7G | ||
| A / - | GpppA | m7GpppA | Cap 0 | ||
| A / G | m7GpppApG | m27,3'-OGpppApG | |||
| A / U | m7GpppApU | m27,3'-OGpppApU | |||
| A / C | |||||
| m2'-OA / - | m7Gpppm2'-OA | Cap 1 | |||
| m2'-OA / G | m7Gpppm2'-OApG | m27,3'-OGpppm2'-OApG | |||
| m2'-OA / U | m7Gpppm2'-OApU | m27,3'-OGpppm2'-OApU | |||
| m2'-OA / C | |||||
| m2N6,2'-OA / - | Cap 1 | ||||
| m2N6,2'-OA / G | m7Gppp m2N6,2'-OApG | m27,3'-OGppp m2N6,2'-OApG | |||
| m2N6,2'-OA / U | |||||
| m2N6,2'-OA / C | |||||
| G / - | GpppG | m7GpppG | m27,3'-OGpppG | m32,2,7GpppG | Cap 0 |
| G / G | |||||
| G / U | |||||
| G / C | |||||
| m2'-OG / - | Cap 1 | ||||
| m2'-OG / G | |||||
| m2'-OG / U | |||||
| m2'-OG / C | |||||
| C / - | m7GpppC | Cap 0 | |||
| C / G | |||||
| C / U | |||||
| C / C | |||||
| m2'-OC / - | Cap 1 | ||||
| m2'-OC / G | |||||
| m2'-OC / U | |||||
| m2'-OC / C | |||||
Products & Ordering
Selected References
[1] Gingras et al. (1999) eIF4 initiation factors: Effectors of mRNA recruitment to ribosomes and regulators of translation. Annu. Rev. Biochem. 68:913.
[2] Izaurralde et al. (1994) A nuclear cap binding protein complex involved in pre-mRNA splicing. Cell 78:657.
[3] Izaurralde et al. (1992) A cap binding protein that may mediate nuclear export of RNA polymerase II-transcribed RNAs. J. Cell Biol. 118:1287.
[4] Beelman et al. (1998) An essential component of the decapping enzyme required for normal rates of mRNA turnover. Nature 382:642.
[5] Paterson et al. (1979) Efficient translation of prokaryotic mRNAs in a eukaryotic cell-free system requires addition of a cap structure. Nature 279:692.
[6] Drummond et al. (1985) The effect of capping and polyadenylation on the stability, movement and translation of synthetic messenger RNAs in Xenopus oocytes. Nucl. Acids Res. 13:375.
[7] Pasquinelli et al. (1995) Reverse 5' caps in RNAs made in vitro by phage RNA polymerases. RNA 1:957.
[8] Grudzien et al. (2007) Synthesis of Anti-Reverse Cap Analogs (ARCAs) and their Applications in mRNA Translation and Stability. Methods Enzymol. 431:203.
