Microbiology
Textbooks
Boundless Microbiology
Microbial Genetics
Translation: Protein Synthesis
Microbiology Textbooks Boundless Microbiology Microbial Genetics Translation: Protein Synthesis
Microbiology Textbooks Boundless Microbiology Microbial Genetics
Microbiology Textbooks Boundless Microbiology
Microbiology Textbooks
Microbiology
Concept Version 9
Created by Boundless

Unsticking Stuck Ribosomes

Ribosomes can get stuck on mRNAs, cells have ways of unsticking them.

Learning Objective

  • Differentiate between nonstop mediated decay and trans-translation as mechanisms of freeing stuck ribosomes


Key Points

    • Due to errors in mRNAs and degradation of mRNAs, ribosomes can stall on transcripts, the stalling of ribosomes can lead to problems for cells.
    • Nonstop mediated decay, involves the binding of a stuck ribosome by proteins, these proteins free the ribosome and lead to the destruction of the mRNA.
    • Trans-translation involves tmRNA an RNA with the properties of both a tRNA and mRNA, which basically convinces the stuck ribosome that the tmRNA is the next codon of the stuck mRNA. The ribosome then translate the tmRNA, which frees the ribosome.

Terms

  • ribosome

    Small organelles found in all cells; involved in the production of proteins by translating messenger RNA.

  • translation

    A process occurring in the ribosome, in which a strand of messenger RNA (mRNA) guides assembly of a sequence of amino acids to make a protein.


Full Text

As mRNAs are transcribed a phenomenon of "stuck" or stalled ribosomes can occur. Stuck mRNA transcripts can arise from many different mechanisms such as premature 3' adenylation or cryptic polyadenylation signals within the coding region of a gene. This lack of a stop codon results a significant issue for cells. Ribosomes translating the mRNA eventually translate into the 3'poly-A tail region of transcripts and stalls. As a result it cannot eject the mRNA. Ribosomes thus may become sequestered associated with the nonstop mRNA and would not be available to translate other mRNA molecules into proteins.

There are two ways in which cells deal with stuck ribosomes, nonstop mediated decay (NSD) and Trans-translation. Nonstop mediated decay mediates this problem by both freeing the stalled ribosomes and marking the nonstop mRNA for degradation in the cell by nucleases. Nonstop mediated decay consists of destroying the nonstop mRNA. The first pathway proteins bind to the stuck ribosome. This binding allows the ribosome to eject the stuck mRNA molecule – this even frees the ribosome and allows it to translate other transcripts. The proteins which freed the ribosome remain with the mRNA which targets the nonstop mRNA for recognition by RNA degradation pathway. NSD is best understood in eukaryotes but similar processes occur in bacteria.

Trans-translation is a recently discovered pathway in E. coli, although it is not completely understood, it involves Transfer-messenger RNA (abbreviated tmRNA) which is a bacterial RNA molecule with dual tRNA-like and messenger RNA-like properties. It is generally agreed that tmRNA first occupies the empty A site of the stalled ribosome. Subsequently, the ribosome moves from the 3' end of the truncated messenger RNA onto the tmRNA where it translates the codons of the tmRNA until the tmRNA stop codon is encountered. Depending on the organism, the resulting truncated protein is degraded and the truncated mRNA . Trans-translation is essential in some bacterial species, whereas other bacteria require tmRNA to survive when subjected to stressful growth conditions.

Trans-translation

rans-Translation stages A through F. A ribosome with its RNA binding sites, designated E, P, and A, is stuck near the 3' end of a broken mRNA. The tmRNP binds to the A-site, allowing the ribosome to switch templates from the broken message onto the open reading frame of the tmRNA via the resume codon (blue GCA). Regular translation eventually resumes. Upon reaching the tmRNA stop codon (red UAA), a hybrid protein with a proteolysis tag (green beads) is released.

[ edit ]
Edit this content
Prev Concept
The Incorporation of Nonstandard Amino Acids
mRNA Processing
Next Concept
Subjects
  • Accounting
  • Algebra
  • Art History
  • Biology
  • Business
  • Calculus
  • Chemistry
  • Communications
  • Economics
  • Finance
  • Management
  • Marketing
  • Microbiology
  • Physics
  • Physiology
  • Political Science
  • Psychology
  • Sociology
  • Statistics
  • U.S. History
  • World History
  • Writing

Except where noted, content and user contributions on this site are licensed under CC BY-SA 4.0 with attribution required.