mRNA quality control and ribosome recycling (lect 13)

Question 1

How is translation normally terminated?

Answer 1

-termination factors recognise stop codons
-RF1 (or 2 in proks) binds to ribosome A site
and triggers peptide hydrolysis (releasing peptide)
-RF3 is recruited to termination complex and releases termination factors (incl. RF1/2) by GTPase activity

Question 2

Why might elongating ribosomes stall?

Answer 2

-mRNA structure (inhibitory secondary structure or bound proteins)
-damage
-deprivation of charged tRNA (eg. if 1 codon repeated lots)
-truncated mRNA (no stop codon)

Question 3

How are stalled ribosomes recovered in E.coli?

Answer 3

trans-translation by tmRNA

Question 4

When is RNA degraded by no-go decay?

Answer 4

when elongating ribosome is stalled (eg. due to structure of mRNA, shortage of tRNAs, etc)

Question 5

When is RNA degraded by non-stop decay?

Answer 5

when mRNA is truncated and there is no stop codon