(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.