This document discusses RNA processing in eukaryotes. It begins by explaining that in eukaryotes, transcription and translation occur in different cellular compartments, while in prokaryotes they occur simultaneously. It then focuses on 5' capping, which is a key part of eukaryotic pre-mRNA processing. 5' capping involves the addition of a 7-methylguanosine residue to the 5' end of nascent mRNA by capping enzymes. This capping protects the mRNA from degradation and aids in transport from the nucleus to the cytoplasm and binding of ribosomes for translation. The capping can involve one or more methylation steps, producing cap0, cap1 or cap2 structures

1. RNA processing
5’ capping
Dr. Emasushan Minj
Assistant Professor
Department of Botany

2. RNA processing
• In eukaryotes, transcription and translation take place in different
cellular compartments like nucleus and cytoplasm respectively.
• In prokaryotes, transcription of mRNA and translation occur
simultaneously. Processing of mRNA undergo little or no
modification.
• In contrast, pre-tRNA and pre-rRNA undergo processing like
cleavage, addition of nucleotides and chemical modification after
synthesis.
• Processing of eukaryotic pre-mRNA involves 5’ capping, 3’
cleavage/polyadenylation, splicing and RNA editing before being
transported to the cytoplasm, where they are translated by
ribosomes.

3. 5’ capping
• Eukaryotic mRNA has peculiar enzymatically appended cap structure, which
consisting of 7-methylguanosine reside joined through 5’-5’ triphosphate
bridge.
• During transcription 7-methylguanosine is added to 5’ end of nascent mRNA.
Capping initiated by dimeric enzyme associated with phosphorylated
carboxyl-terminal tail domain (CTD) of RNA polymerase II.
• One subunit of capping enzyme removes γ-phosphate, another subunit
transfer the GMP of GTP which creates 5’-5’ triphosphate structure.

4. • And final separation of enzyme
transfers methyl groups from s-
adenosylmethionine to the N7
position of the guanine at 5’ end
of RNA.
• If methyl group is present at N7
position called as cap0. This is
the first methylation step and
occurs in all eukaryotes.

5. • In some higher eukaryotes methyl group addition also occurs at
second base, if adenine is present and reaction involves at the N6
position.
• mRNA with methyl groups on the N7 position of the guanine and
the 2’-OH position of the second nucleotide at the 5’ end is
known as cap1.
• Similarly, if methyl group is present at both second and third
nucleotide then it is known as cap2.

6. Functions of 5’ cap
 Protection of mRNA from degradation.
 Transport of the mRNA from nucleus to cytoplasm.
 Binding of ribosome with mRNA.

7. Thank you