Stress granule
Encyclopedia
Stress granules are dense aggregations in the cytosol
composed of proteins & RNAs that appear when the cell
is under stress. The RNA molecules stored are stalled translation
pre-initiation complexes - failed attempts to make protein from mRNA. Stress granules are 100-200 nm in size, not surrounded by membrane
, and associated with the endoplasmatic reticulum. Note that there are also nuclear
stress granules. This article is about the cytosol
ic variety.
Stress granules might also function as a decision point for untranslated mRNAs. Molecules can go down one of three paths: further storage, degradation, or re-initiation of translation
.
The stress proteins that are the main component of stress granules in plant cells are molecular chaperones that sequester, protect, and possibly repair proteins that unfold during heat and other types of stress. Therefore any association of mRNAs with stress granules may simply be a side effect of the association of partially unfolded RNA-binding proteins with stress granules, similar to the association of mRNAs with proteasomes.
of eukaryotic translation initiation factor eIF2α. Further downstream, prion
-like aggregation of the protein TIA-1 leads to the formation of stress granules. The term prion-like is used because aggregation of TIA-1 is concentration
dependent, inhibited by chaperones, and because the aggregates are resistant to proteases. It has also been proposed that microtubules play a role in the formation of stress granules, maybe by transporting granule components. This hypothesis is based on the fact that disruption of microtubules with the chemical nocodazole
blocks the appearance of the granules.
— molecular details of stress granule assembly & function
Laboratories:
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
composed of proteins & RNAs that appear when the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
is under stress. The RNA molecules stored are stalled translation
Translation (genetics)
In molecular biology and genetics, translation is the third stage of protein biosynthesis . In translation, messenger RNA produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein...
pre-initiation complexes - failed attempts to make protein from mRNA. Stress granules are 100-200 nm in size, not surrounded by membrane
Biological membrane
A biological membrane or biomembrane is an enclosing or separatingmembrane that acts as a selective barrier, within or around a cell. It consists of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content...
, and associated with the endoplasmatic reticulum. Note that there are also nuclear
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
stress granules. This article is about the cytosol
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
ic variety.
Proposed functions
The purpose of stress granules might be to protect RNAs from harmful conditions, thus their appearance under stress. The accumulation of RNAs into dense globules could keep them from reacting with harmful chemicals and safe-guard the information coded in their RNA sequence.Stress granules might also function as a decision point for untranslated mRNAs. Molecules can go down one of three paths: further storage, degradation, or re-initiation of translation
Translation (genetics)
In molecular biology and genetics, translation is the third stage of protein biosynthesis . In translation, messenger RNA produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein...
.
The stress proteins that are the main component of stress granules in plant cells are molecular chaperones that sequester, protect, and possibly repair proteins that unfold during heat and other types of stress. Therefore any association of mRNAs with stress granules may simply be a side effect of the association of partially unfolded RNA-binding proteins with stress granules, similar to the association of mRNAs with proteasomes.
Formation of stress granules
Environmental stress triggers a series of signals which eventually lead to formation of stress granules. Early on, it involves phosphorylationPhosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
of eukaryotic translation initiation factor eIF2α. Further downstream, prion
Prion
A prion is an infectious agent composed of protein in a misfolded form. This is in contrast to all other known infectious agents which must contain nucleic acids . The word prion, coined in 1982 by Stanley B. Prusiner, is a portmanteau derived from the words protein and infection...
-like aggregation of the protein TIA-1 leads to the formation of stress granules. The term prion-like is used because aggregation of TIA-1 is concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
dependent, inhibited by chaperones, and because the aggregates are resistant to proteases. It has also been proposed that microtubules play a role in the formation of stress granules, maybe by transporting granule components. This hypothesis is based on the fact that disruption of microtubules with the chemical nocodazole
Nocodazole
Nocodazole is an anti-neoplastic agent which exerts its effect in cells by interfering with the polymerization of microtubules. Microtubules are one type of fibre which constitutes the cytoskeleton, and the dynamic microtubule network has several important roles in the cell, including vesicular...
blocks the appearance of the granules.
Connection with processing bodies
Stress granules and processing bodies share RNA and protein components, both appear under stress, and can physically associate with one another. While stress granules are associated with mRNAs, processing bodies are thought to be places of mRNA degradation. It has been proposed that mRNAs selected for degradation are passed from stress granules to processing bodies.External links
Review articles:— molecular details of stress granule assembly & function
Laboratories: