RNA biology lecture 6

Question 1

Cap snatching by influenza

Answer 1

• Capping confers stability + ensures export from nucleus
• Depends on RNAPII
• Creates issue for virus which transcribe host DNA w/ own polymerase as lack CTD
• RNA virus often replicate in cytoplasm, use cells capping machinery
• Influenza virus = in nucleus, x have CTD, steals cap form emerging pre-mRNA w/ endoribonuc acclivity
• Cap is used as a primer to initiate transcription of its own RNA
• Viral RNA then capped so protected from 5’-3’ degradation + exported to cytoplasm
• Host RNA x have cap, vulnerable to nucleases

Question 2

Capping, early checkpoint release + disease

Answer 2

• Protein encoded by herpes simplex virus inhibits action of CDK9, prevents phosph of Ser 2
• Pol stalls at early checkpoint + x released, host transcripts suppressed

Question 3

Mutations that affect pre-mRNA processing

Answer 3

• Mutations often found in regions needed for processing machinery to assoc w/ pre-mRNA e.g. 5’SS, ESE, 3’SS
• Mutation affecting splice site → ↓ splicing of exons + faulty mRNA
• Mutation in polyA signal ↓ or ↑ cleavage + poly adenyl
• 2 types of mutation: 1. splicing mutation that directly effect consensus signal cause exon skipping, 2. mutation that affect trans-factor so impair splicing machinery
• E.g. fontrotemporal dementia has mutations in MAPT genes
  E,g, Tau enriched in axons, Tau3/4 ration is highly regulated, deviation → accumulation of Tau → neuroses.
• E.g. DMD caused by deletions + mutations e.g. T→A sub in exon 31 that creates an ESS forces exon31 skipping
• Mutation in cis-elements: can promote cancer initiation + progression e.g. KIT oncogene
• Mutation in splicing factors:
• E.g. PWS = ↑ symptoms like restricted growth
• Deletion of paternal SNURF-SnRNP causes PWS by loss of snoRNA, SnoRNA HB11=S2 comp to 5HT2CR pre-mRNA
• PWS = mutation in 5HT2CR, deletion in chromosome 15 that encodes snoRNA inc SNORD115
• SNORD115 assoc w/ exon 5 + suppresses activation of 5a splice site

Question 4

Mis-splicing in cancer

Answer 4

• No. of mutations that inactivate splice sites either directly or indirectly by affecting splice regulatory sequencing
• Mutations to spliceosome e.g. U2AF

Question 5

3’ end formation + disease

Answer 5

• Largely occur in essential cis-elements, leads to Low or Gof
• E.g. thalassemia due to mutation in AATAAA hexamer (recognition signal needed for interaction of CPSF w/ pre-mRNA)
• Mutation in B globin gene Δ hexamer so CPSF x recognise → ↓ B globin protein → aggregation
• Mutation in coagulation factor III where weak consensus site

Question 6

Influenza A virus

Answer 6

• Virus transcribes template, poly-adenyl occurs by transcribing U-rich region in template strand + repeatedly copying U-stretch → export
• mRNA translated to make NS1 which assoc. w/ CPSF1
• AAUAAA in pre-mRNA comprises host mRNA
• NS1 also inhibits splicing by binding + inactivating u6 snRNP