Alarmone

Alarmone is an intracellular signal molecule that is produced due to harsh environmental factors. They regulate the gene expression at transcription level. Alarmones are produced in high concentrations when harsh environmental factors occur in bacteria and plants, such as lack of amino acids to produce proteins. Stringent factors take uncharged tRNA and convert it to an alarmone. Guanosine-5'-triphosphate (GTP) is then converted to 5´-diphosphate 3´-diphosphate guanosine (ppGpp), the archetypical alarmone. ppGpp will bind to RNA polymerase β and β´subunits, changing promoter preference. It will decrease rRNA and other genes transcription but will increase transcription of genes involved in aminoacid biosynthesis and metabolisms involved in famine.