CHAPTER 38RNA Processing in Eukaryotes

Problems: 1-5,7,9-11,14

Primary transcripts are processed.e.g. pre-mRNA is:

• Capped• Poly adenylated

• Spliced

38:1 Processing of Ribosomal RNARNA Pol I

snoRNPs

60S ribosomalSubunit

(also includes a 5S rRNAthat is made by RNA Pol

III)

40S ribosomalsubunit

38:2 Processing of Transfer RNA

• Removal of intron.

• Cleavage of 5’-leader.

• Removal of 3-trailer.

• Addition of –CCA at 3’end.

• Base modification.

RNA Pol III

38:3 Processing of Messenger RNA

Capping

PolyadenylationSplicing

RNA Pol II

Capping

• Guanylate base is methylated at N-7, Step (3)

2-Hydroxyl groups of last two riboses may also be methylated, Step (4)

Increase stability of mRNA.Enhance mRNA translation.

Polyadenylation

(CPSF = cleavage and polyadenylation specificity factor)

Increase stability of mRNA; increase half-life.Enhance mRNA translation.

Splicing of mRNA

Polypyrimidine tract

snRNP

Splicing Mutations → DiseaseAlternative Splicing → Protein

Diversity

2n = different mRNAs (proteins)n = number of alternative splice sites

Transcription and Processing of mRNA are Coupled

CTD (carboxy terminal domain) = -YSPTSPS amino acid sequence at the –COOH terminal of RNA polymerase II. Phosphorylation of the indicated S residues leads the CTD to binding of the factors required for mRNA processing.

The following are all coupled to mRNA transcription:

1. Capping2. Splicing3. Polyadenylation

Post-transcriptional RNA Editing

Stop codon

Lipid transport in the liver-lipids synthesized in the cell.

Synthesized in intestine and transport of dietary lipids chylomicrons.

38:4 Self-Splicing of Messenger RNA

Ribozymes (group 1 type) are catalytic RNAs

Group 2 uses the 2’-OH of an A-residue in the intron instead of a G)

http://ibiomagazine.org/issues/august-issue/discvering-ribozymes.html