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The process of adding a “backwards” (conformationally) guanine to the 5’ end of pre-mRNA; occurs after the first 20-30 nucleotides of mRNA are synthesized
What is 5’ capping?
RNA Triphosphatase removes a the gamma phosphate from the 5’ end of the mRNA, leaving behind 2 phosphates.
What is the first step of 5’ capping?
Guanylyl transferase connects the guanine (monophosphate) to the mRNA using a 5’-5’ triphosphate linkage; during the process, the gamma and beta phosphates are removed from the guan phosphate to become a monophosphate.
What is the second step of 5’ capping?
Methyl transferase methylates the guanine, and sometimes additional methylation occurs.
What is the third step of 5’ capping?
RNA Triphosphatase
Enzyme that removes a phosphate from the 5’ end of the mRNA during 5’ capping
Guanylyl transferase
An enzyme that binds the guanine monophosphate to the 5’ end of the mRNA using a 5’ to 5’ triphosphate linkage; during the process, the guanine loses its gamma and beta phosphates to become monophosphate
Methyl transferase
Enzyme that catalyzes the addition of a methyl group on the guanine monophosphate
protects the mRNA from rapid degeneration (blocks exonucleases)
Facilitates subsequent intron splicing (splicosome recruitment)
Facilitates transport of mRNA out of the nucleus (export recognition, lowers risk of degradation)
Essential for binding the ribosome on the mRNA (ribosomal recognition)
What are the 4 purposes of 5’ capping in eukaryotic mRNA processing?
