Question

2) What are Processing of Eukaryotic Pre-mRNA .

A) How is the 5´-Cap added to nascent RNAs?

B) What proteins are involved in polyadenylation? Indicate their order of association with premRNA and their functions.

Answer 1

there are 3 different processing of Eukaryotic pre-mRNA: 5' Capping, intron splicing, 3' polyadenylation

A)

• Nascent mRNA have triphosphate at the 5' end
• Phosphohydrolase enzyme cleaves one phosphate group from 5’ triphosphate end of mRNA.
• Guanylyl transferase enzyme cleaves two phosphate bonds from the GTP and forms a 5’5’ triphosphate bond with the 5’ end of the mRNA.
• Guanylyl-7-methyl transferase adds a methyl group derived from S-adenosylmethionine in the 7th position of the guanine base
• 2'-O-methyl transferase adds a methyl group at the 2’ OH of the nucleotide adjacent to the cap.

B) The proteins involved in polyadenylation are (in order of association):

• CstF (cleavage stimulation factor) - binds to RNA polymerase and initiates cleavage
• CF I and CF II (Cleavage factor I and II) - binds to RNA and recruit CPSF
• CFSF (cleavage and polyadenylation specificity factor) - catalyzes the cleavage
• PAP (polyadenylate polymerase) - add 80-200 A residues at the 3' end
• PAB II ( polyadenylate binding protein 2) - increases the affinity of polyadenylate polymerase for the RNA