(Science: molecular biology) An unusual small dinucleotides signal molecule produced by bacteria under stress that induces an alteration of metabolism. Many metabolic responses may be altered by a single alarmone. The moleculaes contain multiple phosphate groups between the two nucleotides.
In bacteria when the environment is unfavorable for growth ppGpp and pppGpp are produced. these Alarmones regulate concordantly a large number of cellular activities.