An alarmone is an

intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

signal molecule that is produced in

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

s, and a slim minority of

archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

reacting to harsh

environmental factor An environmental factor, ecological factor or eco factor is any factor, abiotic or biotic, that influences living organisms. Abiotic factors include ambient temperature, amount of sunlight, and pH of the water soil in which an organism lives. Bi ...

s. They regulate the

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

expression at transcription level. Alarmones are produced in high concentrations when harsh environmental factors occur in

and

plants Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...

, such as lack of

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s, to produce

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s. Stringent factors take uncharged

tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ac ...

and convert it to an alarmone.

Guanosine-5'-triphosphate Guanosine-5'-triphosphate (GTP) is a purine nucleoside triphosphate. It is one of the building blocks needed for the synthesis of RNA during the transcription process. Its structure is similar to that of the guanosine nucleoside, the only diff ...

(GTP) is then converted to 5´-diphosphate 3´-diphosphate guanosine (

ppGpp (p)ppGpp, guanosine pentaphosphate and tetraphosphate, also known as the "magic spot" nucleotides, are alarmones involved in the stringent response in bacteria that cause the inhibition of RNA synthesis when there is a shortage of amino acids. ...

), the archetypical alarmone. ppGpp will bind to RNA polymerase β and β´ subunits, changing promoter preference. It will decrease transcription of rRNA and other genes but will increase transcription of genes involved in amino acid biosyntheses and metabolisms involved in famine.

Notes

External links

Alarmone in the Biology Online Dictionary
*{{cite journal , pmid=15109491 , year=2004 , last1=Artsimovitch , first1=I , last2=Patlan , first2=V , last3=Sekine , first3=S , last4=Vassylyeva , first4=MN , last5=Hosaka , first5=T , last6=Ochi , first6=K , last7=Yokoyama , first7=S , last8=Vassylyev , first8=DG , title=Structural basis for transcription regulation by alarmone ppGpp , volume=117 , issue=3 , pages=299–310 , journal=Cell , doi=10.1016/S0092-8674(04)00401-5 , s2cid=17943818 , name-list-style=vanc, doi-access=free RNA