Post-Translational Gene Control (L12)

• stabilizes mRNA (bound by cap-binding complex - protection from degradation) • translation initiation • nuclear export

non-coding nuclear RNAs - mainly pre-mRNAs, but also tRNAs, rRNAs, etc.

hnRNP’s (heterogeneous ribonucleoprotein particles)

extensive B sheets w/ mainly basic (+) aa’s -> interacts w/ negative phosphate backbone of mRNA

• prevent formation of secondary structures in RNA • RNA splicing • transport of mRNA

5’-GU……..A……pyrimidine-rich region…..AG -3’ A = branch point - this nucleotide mediates splicing process

• 2’-OH of branch point A-> nucleophilic attack of phosphodiester bond b/w intron and exon (transesterification) • creates 3’-OH that participates in 2nd nucleophilic attack on splice site -> creates spliced exons + excised lariat intron

snRNA + snRNP

U1: binds 5’ splice site U2: binds sequence including branch point

branch point not included in complementary binding -> A sticks out -> 2’-OH free to act as a nucleophile

U1, U2, U4, U5, U6

carrier of many proteins used for post-translational processing - snRNPs, 5’ cap, poly A tail proteins

exon splicing enhancer - 6 bp long consensus sequence bound by SR proteins, interact w/ each other to help anchor U1 on 5’ splice site and anchor U2 factors

proteins rich in Ser and Arg

cross-exon recognition complex - not put down all in one piece/ at one time

• dsx in drosophila (TRA2 lays down part of spliceosome, but needs TRA - TRA only in females) • B-thallassemia caused by alt splicing defect

IVS - intervening sequence

• 3’ end of pre-mRNA has polyA signal (AAUAAA) - to tell cell to put down a polyA tail • many proteins used to recruit CPSF and CSI • CPSF and CSI bind consensus sequence • facilitate binding of CFII • facilitate binding of PAP • breaks b/w polyA signals • polyA polymerase picks up, starts adding A’s on 3’ end slowly • after 12 A’s, PABPII binds polyA tail -> rapid synthesis

• protects 3’ end of mRNA (prevents nuclease degradation) • increases translation efficiency • participates in nuclear transport

exon junction complex - proteins on 5’ end of each spliced jxn -> marks all jxns b/w exons

5’ cap… 5’ UTR… cds… 3’ UTR…polyA tail

nucleoporins

act as a barrier for the diffusion of large macromolecular complexes

on mature mRNA to help nucleoporin recognize something that needs to be transported to cytoplasm