- Capping is essential for the preparation of mRNA for translation during protein synthesis
- The cap is a modified guanine nucleotide m'G(5')ppp(5')X
- Not only does the process help stabilize the RNA, it aids in the transport to the cytoplasm and promotes the protection against harmful nucleases
- First, a phosphate group is removed by an enzyme at the 5' end
- Second, the addition of GMP to the diphosphate end produced guanonsine 5'5 triphosphate
- Lastly, methyl groups are added promoting recognition of signals
Figure 5. Digital image. Proceedings of the National Academy of Sciences of the United States of America. Web.
- Polyadenylation happens at the end of the 3' pre-mRNA with the addition of polyAs
- First, the pre-mRNA is cleaved when a certain sequence (AAUAA) arrives in the transcript
- RNA polymerase II continues on the template
- RNA made during transcription dissipates, resulting in a cleavage of pre-mRNA that generates a 3' OH group
- The free -OH group extends from enzyme poly(A) polymerase in a reaction that uses ATP
and releases pyrophosphate
Figure 1. Digital image. Genetics. Nature Reviews. Web.