Guanosine pentaphosphate
 |
|
| Names | |
|---|---|
| Other names
guanosine pentaphosphate (pppGpp), guanosine tetraphosphate (ppGpp)
|
|
| Identifiers | |
| DrugBank | |
|
PubChem CID
|
|
| Properties | |
| C10H17N5O17P4 | |
| Molar mass | 603.16 g·mol−1 |
|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|
|
| Infobox references | |
(p)ppGpp, guanosine pentaphosphate or tetraphosphate is an alarmone which is involved in the stringent response in bacteria, causing the inhibition of RNA synthesis when there is a shortage of amino acids present. This causes translation to decrease and the amino acids present are therefore conserved. Furthermore, ppGpp causes the up-regulation of many other genes involved in stress response such as the genes for amino acid uptake (from surrounding media) and biosynthesis.
ppGpp and pppGpp were first identified by Michael Cashel in the 1960s. These nucleotides were found to accumulate rapidly in Escherichia coli cells starved for amino acids, and inhibit synthesis of ribosomal and transfer RNAs. It is now known that (p)ppGpp is also produced in response to other stressors, including carbon and phosphate starvation.
A complete absence of (p)ppGpp causes multiple amino acid requirements, poor survival of aged cultures, aberrant cell division, morphology, and immotility, as well as being locked in a growth mode during entry into starvation.
The synthesis and degradation of (p)ppGpp have been most extensively characterized in the model system E. coli. (p)ppGpp is created via pppGpp synthase, also known as RelA, and is converted from pppGpp to ppGpp via pppGpp phosphohydrolase. RelA is associated with about every one in two hundred ribosomes and it becomes activated when an uncharged transfer RNA (tRNA) molecule enters the A site of the ribosome, due to the shortage of amino acid required by the tRNA. If a mutant bacterium is relA− it is said to be relaxed and no regulation of RNA production due to amino acid absence is seen.
E. coli produces a second protein responsible for degradation of (p)ppGpp, termed SpoT. When the amino acid balance in the cell is restored, (p)ppGpp is hydrolysed by SpoT. This protein also has the capacity to synthesize (p)ppGpp, and seems to be the primary synthase under certain conditions of stress. Most other bacteria encode a single protein that is responsible for both synthesis and degradation of (p)ppGpp, generally homologs of SpoT.
...
Wikipedia