Post-transcriptional Processing

Processing Events in Prokaryotes vs

Eukaryotes

Capping

• RNA Stability– 5'-5' linkage not

recognized by RNAses– Methylation of 2'OH

prevents use of the hydroxyl by RNAses

• Translation efficiency– CAP binding factor part of

translation initiation – eIF4E

Triphosphatase

Guanysyl transferase

Guanosine-7-methyl

transferase

2'-O-methyl transferase

2'-O-methyl transferase

Cleavage and Polyadenylation

Alternative pA Site Usage in Immunoglobulin Genes

Pre-mRNA Splicing

snRNAs & snRNPs: The Splice Girls

• U1 snRNA

• U2 snRNA

• U4 snRNA

• U5 snRNA

• U6 snRNA

• U1 snRNP*

• U2 snRNP

• U4 snRNP

• U5 snRNP

• U6 snRNP

snRNAs associated with various numbers of proteins to form small nuclear ribonucleoprotein complexes

* Pronounced snurps

Splicing• U1 snRNP

– Recognition of 5’ splice site– Interaction with U6 snRNP

• U2 snRNP – Recognition of branch point

sequences– Base pairs with U6 snRNP

• U4 snRNP – Base pairs with U6 & U5 snRNPs

to recruit them to spliceosome• U5 snRNP

– Recognizes last nt in intron & first nucleotide in exon sequences

• U6 snRNP– Displaces U1 at 5' site while base

pairing with U2 – Positions 5' site near branch point

Association of snRNAs with Pre-mRNA

Spliceosomal Complex

Capping and Splicing Occur Co-transcriptionally

Trans-Splicing in C. elegans

• Leader RNA is spliced onto 5' end of multiple pre-mRNAs

Alternative Splicing Regulates Drosophila Sex Determination

Other RNA Processing Events

Ribosomal RNA Processing

Small Nucleolar RNAs - snoRNAs

Some Modified Bases Found in RNA