Stringent Response

The Stringent Response ( German sometimes called " stringent response " or "stringent control") is an adaptation of the metabolism of prokaryotes to an insufficient supply of nutrients such as carbon or amino acids. It is manifested by an increased stress resistance of the cell, a strong slowdown in growth and a significantly reduced metabolism; the cell goes into a kind of hibernation, so to speak.

Pathway

When nutrient deficiency, the signaling molecules guanosine tetraphosphate ( ppGpp ) and Guanosinpentaphosphat ( pppGpp ) are formed from guanosine triphosphate (GTP ) and adenosine triphosphate ( ATP). These molecules act as " alarmones " and influence on a global regulatory network to one third of all the genes in the cell.

In Escherichia coli, this reaction by the two enzymes RelA/L11A ( ppGpp synthase I) and spot ( ppGpp synthase II) is catalyzed. There are at least two ways to trigger the Stringent Response:

• For amino acid starvation remain unloaded in the affected cell tRNAs. These lead to the ribosome in addition to a termination of translation to an activation of RelA, resulting in the formation of ppGpp and pppGpp.
• The formation of pppGpp can also be triggered by SPOT by carbon starvation, but the exact mechanism is still unknown.

Effects

The Stringent Response a number of metabolic processes are carried ppGpp and pppGpp directly inhibited, including via the inhibition of RNA polymerases, the synthesis of RNA and protein biosynthesis. In addition, a number of biosynthetic and catabolic operons enabled in order to use other nutrient sources.

Are further inhibited through different signal transduction pathways in the synthesis of phospholipids and nucleotides, as well as cell division. On the other hand, the transcription accuracy is increased, including increased synthesis of proteins for stress - combating chaperones and promoted protein degradation.