The ''chrB''-a RNA motif and ''chrB''-b RNA motif refer to a related, conserved

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

structure that was discovered by bioinformatics. The structures of these motifs are similar, and some genomic locations are predicted to exhibit both motifs. The ''chrB''-b motif has an extra

pseudoknot __NOTOC__ A pseudoknot is a nucleic acid secondary structure containing at least two stem-loop structures in which half of one stem is intercalated between the two halves of another stem. The pseudoknot was first recognized in the turnip yellow ...

that is not consistently found in ''chrB''-a examples. It was proposed that the two motifs could be unified into one common structure, with additional information. Both motifs are found in

Alphaproteobacteria ''Alphaproteobacteria'' or ''α-proteobacteria'', also called ''α-Purple bacteria'' in earlier literature, is a class of bacteria in the phylum '' Pseudomonadota'' (formerly "Proteobacteria"). The '' Magnetococcales'' and '' Mariprofundales'' ar ...

and likely function as

cis-regulatory element ''Cis''-regulatory elements (CREs) or ''cis''-regulatory modules (CRMs) are regions of non-coding DNA which regulate the transcription of neighboring genes. CREs are vital components of genetic regulatory networks, which in turn control morpho ...

s, in view of their positions upstream of protein-coding

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

s. Additionally, the Shine-Dalgarno sequence of the genes is a part of the conserved

secondary structure Protein secondary structure is the local spatial conformation of the polypeptide backbone excluding the side chains. The two most common Protein structure#Secondary structure, secondary structural elements are alpha helix, alpha helices and beta ...

of the ''chrB'' motifs. Thus, a stabilization of this secondary structure is expected to reduce gene expression. The genes apparently regulated by these RNAs share a relationship with each other in that they are involved in resistance to toxic levels of

chromate Chromate or chromat, and their derived terms, may refer to: Chemistry * Chromate and dichromate, ions * Monochromate, an ion * Trichromate, an ion * Tetrachromate, an ion * Chromate conversion coating, a method for passivating metals Biolog ...

: * Many of these genes are classified as the gene ''chrB'', which was found to improve the resistance of '' Ochrobactrum tritici'' to chromate. * Genes classified as ''chrA'' are also common. * Genes that encode the

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

superoxide dismutase Superoxide dismutase (SOD, ) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide () anion radical into normal molecular oxygen (O2) and hydrogen peroxide (). Superoxide is produced as a by-product of oxy ...

are also common, and this gene also has an established role in chromate resistance. * Rarely regulated genes with and without a relationship to chromate were also discussed. Additionally, a ''chrB'' gene regulated by a ''chrB''-a RNA in ''

Sinorhizobium meliloti ''Ensifer meliloti'' (formerly ''Rhizobium meliloti'' and ''Sinorhizobium meliloti'') are an aerobic, Gram-negative, and diazotrophic species of bacteria. ''S. meliloti'' are motile and possess a cluster of peritrichous flagella. ''S. melilo ...

'' strain 1021 is highly expressed in bacteria growing on plants.

References

{{reflist Non-coding RNA