In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splicing to create monocistronic mRNAs that are translated separately, i.e. several strands of mRNA that each encode a single gene product. The result of this is that the genes contained in the operon are either expressed together or not at all. Several genes must be co-transcribed to define an operon.
Ribozymes are RNA molecules that have the ability to catalyze specific biochemical reactions, including RNA splicing in gene expression, similar to the action of protein enzymes. The 1982 discovery of ribozymes demonstrated that RNA can be both genetic material and a biological catalyst, and contributed to the RNA world hypothesis, which suggests that RNA may have been important in the evolution of prebiotic self-replicating systems.
In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a common three-dimensional structure that appears in a variety of different, evolutionarily unrelated molecules. A structural motif does not have to be associated with a sequence motif; it can be represented by different and completely unrelated sequences in different proteins or RNA.
Ribonuclease H is a family of non-sequence-specific endonuclease enzymes that catalyze the cleavage of RNA in an RNA/DNA substrate via a hydrolytic mechanism. Members of the RNase H family can be found in nearly all organisms, from bacteria to archaea to eukaryotes.
A structural gene is a gene that codes for any RNA or protein product other than a regulatory factor. A term derived from the lac operon, structural genes are typically viewed as those containing sequences of DNA corresponding to the amino acids of a protein that will be produced, as long as said protein does not function to regulate gene expression. Structural gene products include enzymes and structural proteins. Also encoded by structural genes are non-coding RNAs, such as rRNAs and tRNAs.
In genetics, attenuation is a regulatory mechanism for some bacterial operons that results in premature termination of transcription. The canonical example of attenuation used in many introductory genetics textbooks, is ribosome-mediated attenuation of the trp operon. Ribosome-mediated attenuation of the trp operon relies on the fact that, in bacteria, transcription and translation proceed simultaneously. Attenuation involves a provisional stop signal (attenuator), located in the DNA segment that corresponds to the leader sequence of mRNA. During attenuation, the ribosome becomes stalled (delayed) in the attenuator region in the mRNA leader. Depending on the metabolic conditions, the attenuator either stops transcription at that point or allows read-through to the structural gene part of the mRNA and synthesis of the appropriate protein.
The trp operon is a group of genes that are transcribed together, encoding the enzymes that produce the amino acid tryptophan in bacteria. The trp operon was first characterized in Escherichia coli, and it has since been discovered in many other bacteria. The operon is regulated so that, when tryptophan is present in the environment, the genes for tryptophan synthesis are repressed.
Protoporphyrin ferrochelatase (EC 4.98.1.1, formerly EC 4.99.1.1, or ferrochelatase; systematic name protoheme ferro-lyase (protoporphyrin-forming)) is an enzyme encoded by the FECH gene in humans. Ferrochelatase catalyses the eighth and terminal step in the biosynthesis of heme, converting protoporphyrin IX into heme B. It catalyses the reaction:
Amino acid synthesis is the set of biochemical processes by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to synthesize all amino acids. For example, humans can synthesize 11 of the 20 standard amino acids. These 11 are called the non-essential amino acids).
The Tryptophan operon leader is an RNA element found at the 5′ of some bacterial tryptophan operons. The leader sequence can form two different structures known as the terminator and the anti-terminator, based on the Tryptophan amounts in the cell. The leader also codes for very short peptide sequence that is rich in tryptophan. The terminator structure is recognised as a termination signal for RNA polymerase and the operon is not transcribed. This structure forms when the cell has an excess of tryptophan and ribosome movement over the leader transcript is not impeded. When there is a deficiency of the charged tryptophanyl tRNA the ribosome translating the leader peptide stalls and the antiterminator structure can form. This allows RNA polymerase to transcribe the operon.
The FMN riboswitch is a highly conserved RNA element which is naturally occurring, and is found frequently in the 5'-untranslated regions of prokaryotic mRNAs that encode for flavin mononucleotide (FMN) biosynthesis and transport proteins. This element is a metabolite-dependent riboswitch that directly binds FMN in the absence of proteins, thus giving it the ability to regulate RNA expression by responding to changes in the concentration of FMN. In Bacillus subtilis, previous studies have shown that this bacterium utilizes at least two FMN riboswitches, where one controls translation initiation, and the other controls premature transcription termination. Regarding the second riboswitch in Bacilius subtilis, premature transcription termination occurs within the 5' untranslated region of the ribDEAHT operon, precluding access to the ribosome-binding site of ypaA mRNA. FMN riboswitches also have various magnesium and potassium ions dispersed throughout the nucleotide structure, some of which participate in binding of FMN.
The PreQ1-I riboswitch is a cis-acting element identified in bacteria which regulates expression of genes involved in biosynthesis of the nucleoside queuosine (Q) from GTP. PreQ1 (pre-queuosine1) is an intermediate in the queuosine pathway, and preQ1 riboswitch, as a type of riboswitch, is an RNA element that binds preQ1. The preQ1 riboswitch is distinguished by its unusually small aptamer, compared to other riboswitches. Its atomic-resolution three-dimensional structure has been determined, with the PDB ID 2L1V.
Usually found in gram-positive bacteria, the T box leader sequence is an RNA element that controls gene expression through the regulation of translation by binding directly to a specific tRNA and sensing its aminoacylation state. This interaction controls expression of downstream aminoacyl-tRNA synthetase genes, amino acid biosynthesis, and uptake-related genes in a negative feedback loop. The uncharged tRNA acts as the effector for transcription antitermination of genes in the T-box leader family. The anticodon of a specific tRNA base pairs to a specifier sequence within the T-box motif, and the NCCA acceptor tail of the tRNA base pairs to a conserved bulge in the T-box antiterminator hairpin.
The Ykok leader or M-box is a Mg2+-sensing RNA structure that controls the expression of Magnesium ion transport proteins in bacteria. It is a distinct structure to the Magnesium responsive RNA element.
Nucleic acid analogues are compounds which are analogous to naturally occurring RNA and DNA, used in medicine and in molecular biology research. Nucleic acids are chains of nucleotides, which are composed of three parts: a phosphate backbone, a pentose sugar, either ribose or deoxyribose, and one of four nucleobases. An analogue may have any of these altered. Typically the analogue nucleobases confer, among other things, different base pairing and base stacking properties. Examples include universal bases, which can pair with all four canonical bases, and phosphate-sugar backbone analogues such as PNA, which affect the properties of the chain . Nucleic acid analogues are also called Xeno Nucleic Acid and represent one of the main pillars of xenobiology, the design of new-to-nature forms of life based on alternative biochemistries.
Rsa RNAs are non-coding RNAs found in the bacterium Staphylococcus aureus. The shared name comes from their discovery, and does not imply homology. Bioinformatics scans identified the 16 Rsa RNA families named RsaA-K and RsaOA-OG. Others, RsaOH-OX, were found thanks to an RNomic approach. Although the RNAs showed varying expression patterns, many of the newly discovered RNAs were shown to be Hfq-independent and most carried a C-rich motif (UCCC).
Mycobacterium tuberculosis contains at least nine small RNA families in its genome. The small RNA (sRNA) families were identified through RNomics – the direct analysis of RNA molecules isolated from cultures of Mycobacterium tuberculosis. The sRNAs were characterised through RACE mapping and Northern blot experiments. Secondary structures of the sRNAs were predicted using Mfold.
RegulonDB is a database of the regulatory network of gene expression in Escherichia coli K-12. RegulonDB also models the organization of the genes in transcription units, operons and regulons. A total of 120 sRNAs with 231 total interactions which all together regulate 192 genes are also included. RegulonDB was founded in 1998 and also contributes data to the EcoCyc database.
In molecular biology, the SR1 RNA is a small RNA (sRNA) produced by species of Bacillus and closely related bacteria. It is a dual-function RNA which acts both as a protein-coding RNA and as a regulatory sRNA.
Transcription-translation coupling is a mechanism of gene expression regulation in which synthesis of an mRNA (transcription) is affected by its concurrent decoding (translation). In prokaryotes, mRNAs are translated while they are transcribed. This allows communication between RNA polymerase, the multisubunit enzyme that catalyzes transcription, and the ribosome, which catalyzes translation. Coupling involves both direct physical interactions between RNA polymerase and the ribosome, as well as ribosome-induced changes to the structure and accessibility of the intervening mRNA that affect transcription.
