An evolutionarily conserved family of signaling molecules, TGF-β superfamily includes: 

TGF-β family, Nodal and activin families, BMPs, Vg1 family, GDNF, AMH

TLS Online TPP Program

#Id: 6656

#Unit 3. Fundamental Processes

Shortly after transcription initiation, Pol II is paused 30 nucleotides downstream from the initiation site, waiting for the recruitment of the capping enzymes to add the cap to the 5’ end of nascent RNA. Without this protection, nascent RNA may be vulnerable to attack by 5’–3’ exonucleases, and such trimming may induce the Pol II complex to fall off of the DNA template.

TLS Online TPP Program

#Id: 6657

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6658

#Unit 3. Fundamental Processes

In the nucleus, the cap is recognized and bound by the cap binding CBP20/80 heterodimer. This binding event stimulates splicing of the first intron and, via a direct interaction with the mRNA export machinery (TREX complex), facilitates mRNA export out of the nucleus. Once reaching the cytoplasm, a different set of proteins (eIF4F) binds the cap to initiate translation of the mRNA in the cytoplasm.

TLS Online TPP Program

#Id: 6659

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6660

#Unit 3. Fundamental Processes

The sequence AAUAAA is a signal for cleavage to generate a 3’ end of mRNA that is polyadenylated. Addition of poly(A) to nuclear RNA can be prevented by the analog 3’–deoxyadenosine known as cordycepin

TLS Online TPP Program

#Id: 6661

#Unit 3. Fundamental Processes

The site of cleavage/polyadenylation in most pre-mRNAs is flanked by two cis-acting signals:  An upstream AAUAAA motif, which is usually located 11 to 30 nucleotides from the site, and  A downstream U-rich or GU-rich element. 

he AAUAAA is needed for cleavage and polyadenylation because deletion or mutation of the AAUAAA hexamer prevents generation of the polyadenylated 3’ end