(p)ppGpp (collective for ppGpp and pppGpp) is a nucleotide based second messenger and a key regulator of stringent stress response in many bacteria. During nutritional starvation (p)ppGpp initiates the switch from bacterial growth into survival mode. Growth is arrested as (p)ppGpp binds RNA polymerase (RNAP) leading to repressed transcription rate of stable RNA (rRNA, tRNA). Instead, transcription of genes involved in biosynthesis of amino acids is enhanced, leading to prolonged survival.
 Hauryliuk et al. (2015) Recent functional insights into the role of (p)ppGpp in bacterial physiology. Nature Reviews Microbiology 13 (5):298.
 Dalebroux et al. (2012) ppGpp: magic beyond RNA polymerase. Nature Reviews Microbiology 10 (3):203.