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