POST-TRANSCRIPTIONAL MODIFICATIONS:

• Help with the export of the mRNA from the nucleus
• Protect the mRNA from degradation in the cytoplasm
• Help facilitate proper translation

3 TYPES OF MODIFICATIONS

• 5′ capping
• Poly-A tail
• Intron splicing

5′ capping

• Modified guanine nucleotide
• Added to 5′ end of RNA molecule
• Added during transcription

Poly-A tail

• Multiple adenines added at the end of the polyadenylation signal
• Added to the 3′ end of the RNA

Intron splicing

Intron

Sections of the RNA sequence that are found in between exons

• Introns are removed from the RNA by the spliceosome

Spliceosome

Group of small nuclear RNAs and proteins which join together to recognize and remove introns from transcribed RNA

• Products of intron splice are mature mRNA and circular intron

Alternative splicing allows for one gene to code for multiple, similar proteins

Incorrect splicing is often the cause of the disease Hutchinson-Gilford progeria syndrome

DIFFERENCES BETWEEN PROKARYOTIC AND EUKARYOTIC TRANSCRIPTION

Prokaryotes:

• Only one polymerase isoform
• Occurs in the cytoplasm (since no nucleus)
• RNA polymerase recognizes the promoter sequence
• RNA polymerase recognizes the terminator sequence
• No additional processing of mRNA