BIOL 300 Discussion - RNA Processing

what is the process of expression in eukaryotes?

DNA is bound by RNA poly, resulting in pre-mRNA. it’s processed by splicing, adding polyA tail (polyadenylation), and 5’ cap inside the nucleus. the mRNA can then go into the cytoplasm to be met by ribosomes and build polypeptide chains with tRNA

what are the 3 modifications for eukaryotic pre-mRNA?

capping, splicing, polyadenylation

what is the function of guanylyl transferase?

adds methylated guanine at 5’ end of mRNA

what proteins are involved in polyadenylation?

CPSF, CstF, CFI and CFII, PAP, PABP

what is the process of capping?

phosphorylated CTD of RNA polymerase recruits guanylyl transferase, which attaches a GMP to a modified 5’ of RNA. phosphorylated CTD then recruits CPSF which recruitss CstF

what does CPSF (Cleavage and polyadenylation factor) do?

recognizes AAUAAA sequence, which is a seq that binds to proteins that facilitate the cleavage of pre-mRNA and the subsequent addition of a poly(A) tail

what does CstF (Cleavage Stimulatory Factor) do?

binds to CPSF and recruits endonucleases CFI and CFII

what do CFI and CFII (cleavage factor 1 and 2) do?

cleaves the RNA

what does PAP (PolyA polymerase) do?

binds to 3’ end and adds ~200 adenines

what does PABP (polyA binding protein) do?

binds to poly a tail and confers message stability to help with translation

which RNA polymerase has phosphorylated CTD?

RNA Poly II

what is the recognition site for CPSF?

AAUAAA

whats the process for creating a poly A tail? (polyadenylation)

CPSF recognizes AAUAAA sequence, and CstF binds to CPSF and recruits CF I and CFII, then PAP binds to 3’ end and synthesizes adenine tail. PABP binds to polyA tail to make sure it’s stable, and the exonucleaes remove excess nucleotides

what splices pre-mRNA?

spliceosome - made of snRNPs

what are snRNPs?

small nuclear ribonucleoproteins - has 1 RNA protein, 8 common snRNP proteins, and 12 proteins unique to that snRNP

what are the steps of splicing?

E complex (has a GU donor sequence seq, branch point, and AG acceptor site), then A complex (everythings gone beside U1, and U2 moved to branch point and commits pre-mRNA to splicing pathway by recognizing proper donor site. then, B1 ( u5-u4/u6 timer binds), b2 (u1 and u4 are released and u5 and u6 are positioned, with u6 going from exon to intron seq at donor site). Finally the last two events are cleavage events with C1 and C2 complex

what is alternative splicing?

when pre-mRNA is spliced in different ways to produce different products.

what degrades prokaryotic message?

when ribosomes aren’t densely packed

what degrades eukaryotic message?

tail is shorted to around 10 adenines

what structure allows for stability in prokaryotes?

stem loop

what structure allows for stability in eukaryotes?

polyS tail and G-Cap

what structure controls RNA degredation in prokaryotes?

degradosome - made up of RNAse E, RhiB (helicase), PNPase (exonuclease), and Enolase (reg. subunit)

what is the process for RNA prokaryotic degredation?

PABP is removed by polyA nuclease, Lms1-7 binds to poly A tail, DCP is recruited

what is the process for RNA eukaryotic degredation?

starts with PABP being removed by PoyA nuclease, then the exosome binds to polyA tail. then, exosome functions like prokaryotic degrasome

what is the process for RNA silencing?

A miRNA is produced and loaded into the RISC complex (RNA-Induced Silencing Complex). The, miRNA pairs with a complementary mRNA sequence. Depending on how well they match:

• Perfect match: RISC cuts the mRNA → degradation.

• Imperfect match: RISC blocks translation or triggers deadenylation → gradual decay.