The SAM-Chlorobi RNA motif is a conserved RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 structure that was identified by bioinformatics

Bioinformatics

Bioinformatics is the application of computer science and information technology to the field of biology and medicine. Bioinformatics deals with algorithms, databases and information systems, web technologies, artificial intelligence and soft computing, information and computation theory, software...

. The RNAs are found only in bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 classified as within the phylum

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

 Chlorobi. These RNAs are always in the 5' untranslated regions of operon

Operon

In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create...

s that contain metK and ahcY genes. metK genes encode methionine adenosyltransferase

Methionine adenosyltransferase

Methionine adenosyltransferase is an enzyme which catalyses the synthesis of S-adenosylmethionine from methionine and ATP.-External links:...

, which synthesizes S-adenosyl methionine

S-Adenosyl methionine

S-Adenosyl methionine is a common cosubstrate involved in methyl group transfers. SAM was first discovered in Italy by G. L. Cantoni in 1952. It is made from adenosine triphosphate and methionine by methionine adenosyltransferase . Transmethylation, transsulfuration, and aminopropylation are the...

 (SAM), and ahcY genes encode S-adenosylhomocysteine hydrolase, which degrade the related metabolite S-Adenosyl-L-homocysteine

S-adenosyl-L-homocysteine

S-Adenosyl-L-homocysteine is an amino acid derivative used in several metabolic pathways in most organisms. It is an intermediate in the synthesis of cysteine and adenosine....

 (SAH). In fact all predicted metK and ahcY genes within Chlorobi bacteria as of 2010 are preceded by predicted SAM-Chlorobi RNAs. Predicted promoter sequences are consistently found upstream of SAM-Chlorobi RNAs, and these promoter sequences imply that SAM-Chlorobi RNAs are indeed transcribed as RNAs. The promoter sequences are commonly associated with strong transcription in the phyla Chlorobi and Bacteroidetes

Bacteroidetes

The phylum Bacteroidetes is composed of three large classes of bacteria that are widely distributed in the environment, including in soil, in sediments, sea water and in the guts and on the skin of animals....

, but are not used by most lineages of bacteria. The placement of SAM-Chlorobi RNAs suggests that they are involved in the regulation of the metK/ahcY operon through an unknown mechanism.