The 5′ untranslated region is the region of a messenger RNA (mRNA) that is directly upstream from the initiation codon. This region is important for the regulation of translation of a transcript by differing mechanisms in viruses, prokaryotes and eukaryotes. While called untranslated, the 5′ UTR or a portion of it is sometimes translated into a protein product. This product can then regulate the translation of the main coding sequence of the mRNA. In many organisms, however, the 5′ UTR is completely untranslated, instead forming a complex secondary structure to regulate translation.
Red clover necrotic mosaic virus (RCNMV) contains several structural elements present within the 3′ and 5′ untranslated regions (UTR) of the genome that enhance translation. In eukaryotes transcription is a prerequisite for translation. During transcription the pre-mRNA transcript is processes where a 5′ cap is attached onto mRNA and this 5′ cap allows for ribosome assembly onto the mRNA as it acts as a binding site for the eukaryotic initiation factor eIF4F. Once eIF4F is bound to the mRNA this protein complex interacts with the poly(A) binding protein which is present within the 3′ UTR and results in mRNA circularization. This multiprotein-mRNA complex then recruits the ribosome subunits and scans the mRNA until it reaches the start codon. Transcription of viral genomes differs from eukaryotes as viral genomes produce mRNA transcripts that lack a 5’ cap site. Despite lacking a cap site viral genes contain a structural element within the 5’ UTR known as an internal ribosome entry site (IRES). IRES is a structural element that recruits the 40s ribosome subunit to the mRNA within close proximity of the start codon.
The Actino-pnp RNA motif is a conserved structure found in Actinomycetota that is apparently in the 5' untranslated regions of genes predicted to encode exoribonucleases. The RNA element's function is likely analogous to an RNA structure found upstream of polynucleotide phosphorylase genes in E. coli and related enterobacteria. In this latter system, the polynucleotide phosphorlyase gene regulates its own expression levels by a feedback mechanism that involves its activity upon the RNA structure. However, the E. coli RNA appears to be structurally unrelated to the Actino-pnp motif.
The asd RNA motif is a conserved RNA structure found in certain lactic acid bacteria. The asd motif was detected by bioinformatics and an individual asd RNA in Streptococcus pyogenes was detected by microarray and northern hybridization experiments as a 170-nucleotide molecule called "SR914400". The transcription start site determined for SR914400 corresponds to the 5′-end of the molecule shown in the consensus diagram.
The Chlorobi-RRM RNA motif is a conserved RNA structure identified by bioinformatics. It is found within bacteria in the phylum Chlorobiota, and is exclusively detected in the presumed 5' untranslated regions of genes that encode putative RNA-binding proteins. Since many RNA-binding proteins regulate their own expression in a feedback mechanism by binding or acting up their 5' UTR, it was proposed that the Chlorobi-RRM is a component in an analogous feedback mechanism. Structurally, the motif consists of two stem-loops, the second of which might function as a rho-independent transcription terminator.
The Downstream-peptide motif refers to a conserved RNA structure identified by bioinformatics in the cyanobacterial genera Synechococcus and Prochlorococcus and one phage that infects such bacteria. It was also detected in marine samples of DNA from uncultivated bacteria, which are presumably other species of cyanobacteria.
The glutamine riboswitch is a conserved RNA structure that was predicted by bioinformatics. It is present in a variety of lineages of cyanobacteria, as well as some phages that infect cyanobacteria. It is also found in DNA extracted from uncultivated bacteria living in the ocean that are presumably species of cyanobacteria.
The gyrA RNA motif is a conserved RNA structure identified by bioinformatics. The RNAs are present in multiple species of bacteria within the order Pseudomonadales. This order contains the genus Pseudomonas, which includes the opportunistic human pathogen Pseudomonas aeruginosa and Pseudomonas syringae, a plant pathogen.
The JUMPstart RNA motif describes a conserved RNA-based secondary structure associated with JUMPstart elements. The 39-base-pair JUMPstart sequence describes a conserved element upstream of genes that participate in polysaccharide synthesis. The JUMPstart element has been shown to function as an RNA, and is present in the 5' untranslated regions of the genes it regulates.
The Lacto-rpoB RNA motif is a conserved RNA structure identified by bioinformatics. It has been detected only in lactic acid bacteria, and is always located in the presumed 5' untranslated regions of rpoB genes. These genes encode a subunit of RNA polymerase, and it is hypothesized that Lacto-rpoB RNA participate in the regulation of these genes.
The Lacto-usp RNA motif is a conserved RNA structure identified in bacteria by bioinformatics. Lacto-usp RNAs are found exclusively in lactic acid bacteria, and exclusively in the possible 5′ untranslated regions of operons that contain a hypothetical gene and a usp gene. The usp gene encodes the universal stress protein. It was proposed that the Lacto-usp might correspond to the 6S RNA of the relevant species, because four of five of these species lack a predicted 6S RNA, and 6S RNAs commonly occur in 5′ UTRs of usp genes. However, given that the Lacto-usp RNA motif is much shorter than the standard 6S RNA structure, the function of Lacto-usp RNAs remains unclear.
The livK RNA motif describes a conserved RNA structure that was discovered using bioinformatics. The livK motif is detected only in the species Pseudomonas syringae. It is found in the potential 5' untranslated regions of livK genes and downstream livM and livH genes, as well as the 5' UTRs of amidase genes. The liv genes are predicted to be transporters of branched-chain amino acids, i.e., leucine, isoleucine or valine. The specific reaction catalyzed the amidase genes is not predicted.
The msiK RNA motif describes a conserved RNA structure discovered using bioinformatics. The RNA is always found in the presumed 5' untranslated regions of genes annotated as msiK, and is therefore hypothesized to be an RNA-based cis-regulatory element that regulates these genes.
The nuoG RNA motif is a conserved RNA structure detected by bioinformatics. It is located in the presumed 5' untranslated regions of nuoG genes. This gene and the downstream genes probably comprise an operon that encodes various subunits of ubiquinone reductase enzyme.
PhotoRC RNA motifs refer to conserved RNA structures that are associated with genes acting in the photosynthetic reaction centre of photosynthetic bacteria. Two such RNA classes were identified and called the PhotoRC-I and PhotoRC-II motifs. PhotoRC-I RNAs were detected in the genomes of some cyanobacteria. Although no PhotoRC-II RNA has been detected in cyanobacteria, one is found in the genome of a purified phage that infects cyanobacteria. Both PhotoRC-I and PhotoRC-II RNAs are present in sequences derived from DNA that was extracted from uncultivated marine bacteria.
The psaA RNA motif describes a class of RNAs with a common secondary structure. psaA RNAs are exclusively found in locations that presumably correspond to the 5' untranslated regions of operons formed of psaA and psaB genes. For this reason, it was hypothesized that psaA RNAs function as cis-regulatory elements of these genes. The psaAB genes encode proteins that form subunits in the photosystem I structure used for photosynthesis. psaA RNAs have been detected only in cyanobacteria, which is consistent with their association with photosynthesis.
The rmf RNA motif is a conserved RNA structure that was originally detected using bioinformatics. rmf RNAs are consistently foundwithin species classified into the genus Pseudomonas, and is located potentially in the 5′ untranslated regions of rmf genes. These genes encodes the ribosome modulation factor protein, which affects the translation of genes by modifying ribosome structure in response to stress such as starvation. This ribosome modulation is a part of the stringent response in bacteria. The likely biological role of rmf RNAs is ambiguous. Since the RNA could be in the 5′ UTRs of protein-coding genes, it was hypothesized that it functions as a cis-regulatory element. This hypothesis is bolstered by the observation that ribosome modulation factor binds ribosomal RNA, and many cis-regulatory RNAs called ribosomal protein leaders participate in a feedback regulation mechanism by binding to proteins that normally bind to ribosomal RNA. However, since rmf RNAs are not very close to the rmf genes, they might function as non-coding RNAs.
The rne-II RNA motif is a conserved RNA structure identified using bioinformatics. It is detected only in species classified within the family Pseudomonadaceae, a group of gammaproteobacteria. rne-II RNAs are consistently located in the presumed 5' untranslated regions of genes that encode Ribonuclease E. The RNase E 5' UTR element is a previously identified RNA structure that is also found in the 5' UTRs of RNase E genes. However, the latter motif is found only in enterobacteria, and the two motifs have apparently unrelated structure. In view of their differences, it was hypothesized that rne-II RNAs fulfill the same functional role as RNase E 5' UTR elements, which is to regulate the levels of RNase E proteins by acting as a substrate for RNase E. Thus, when concentrations of RNase E are high, they will degrade their own messenger RNA.
The yjdF RNA motif is a conserved RNA structure identified using bioinformatics. Most yjdF RNAs are located in bacteria classified within the phylum Bacillota. A yjdF RNA is found in the presumed 5' untranslated region of the yjdF gene in Bacillus subtilis, and almost all yjdF RNAs are found in the 5' UTRs of homologs of this gene. The function of the yjdF gene is unknown, but the protein that it is predicted to encode is classified by the Pfam Database as DUF2992.
The S4 ribosomal protein leader is a ribosomal protein leader involved in ribosome biogenesis. It is used as an autoregulatory mechanism to control the concentration of the ribosomal protein S4. Two examples of such leaders that use different conserved structures, in Bacillota and Gammaproteobacteria, have been experimentally confirmed. Four additional S4 ribosomal protein leaders, each with distinct structures, were predicted in various bacteria phyla. In Bacteroidia or Bacillota, the structure is located in the 5′ untranslated regions of mRNAs encoding ribosomal proteins S4 (rpsD), RNA polymerase alpha subunit (rpoA) and L17 (rplQ). In Clostridia and Gammaproteobacteria, the ribosomal proteins S13 (rpsM) and S11 (rpsK) were also part of the mRNA encoding region.
