Medullary collecting duct is permeable to urea, and there are special urea transporters that facilitate urea diffusion across the luminal and basolateral membranes

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

TLS Online TPP Program

#Id: 6662

#Unit 3. Fundamental Processes

Ser2 phosphatase Fcp1 regenerates RNA Pol II pool