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Sigma Factor
A sigma factor (σ factor or specificity factor) is a protein needed for initiation of Transcription (biology), transcription in bacteria. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase (RNAP) to gene promoter (biology), promoters. It is homologous to archaeal transcription factor B and to Eukaryote, eukaryotic factor TFIIB. The specific sigma factor used to initiate transcription of a given gene will vary, depending on the gene and on the environmental signals needed to initiate transcription of that gene. Selection of promoters by RNA polymerase is dependent on the sigma factor that associates with it. They are also found in plant chloroplasts as a part of the bacteria-like plastid-encoded polymerase (PEP). The sigma factor, together with RNA polymerase, is known as the RNA polymerase Enzyme#Cofactors, holoenzyme. Every molecule of RNA polymerase holoenzyme contains exactly one sigma factor subunit, which in the model bacterium '' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transcription (biology)
Transcription is the process of copying a segment of DNA into RNA for the purpose of gene expression. Some segments of DNA are transcribed into RNA molecules that can encode proteins, called messenger RNA (mRNA). Other segments of DNA are transcribed into RNA molecules called non-coding RNAs (ncRNAs). Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a Complementarity (molecular biology), complementary language. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, Antiparallel (biochemistry), antiparallel RNA strand called a primary transcript. In virology, the term transcription is used when referring to mRNA synthesis from a viral RNA molecule. The genome of many Orthornavirae, RNA viruses is composed of Sense (molecular biology), negative-sense RNA which acts as a template for positive sense viral messenger RNA - a necessary step in the synthesis of viral proteins needed for viral replication. This process ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RpoE
The gene ''rpoE'' (RNA polymerase, extracytoplasmic E) encodes the sigma factor ''sigma-24'' (σ24, sigma E, or RpoE), a protein in ''Escherichia coli'' and other species of bacteria. Depending on the bacterial species, this gene may be referred to as ''sigE''. RpoE appears to be necessary for the exocytoplasmic stress response. ''E. coli'' mutants without ''rpoE'' cannot grow at high temperatures (that is, above 42 degrees C) and show growth defects at lower temperatures, though this may be due to compensatory mutations. In some bacterial species, such as ''Clostridium botulinum'', this sigma factor may be necessary for sporulation In biology, a spore is a unit of sexual (in fungi) or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plant .... The stress response regulation activities of RpoE are modulated by the Hfq protein in ''E. coli''. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluorescence Resonance Energy Transfer
Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colored visible light. The color of the light emitted depends on the chemical composition of the substance. Fluorescent materials generally cease to glow nearly immediately when the radiation source stops. This distinguishes them from the other type of light emission, phosphorescence. Phosphorescent materials continue to emit light for some time after the radiation stops. This difference in duration is a result of quantum spin effects. Fluorescence occurs when a photon from incoming radiation is absorbed by a molecule, exciting it to a higher energy level, followed by the emission of light as the molecule returns to a lower energy state. The emitted light may have a longer wavelength and, therefore, a lower photon energy than the absorbed radi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Holoenzyme
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 molecules known as product (chemistry), products. Almost all metabolism, metabolic processes in the cell (biology), cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps. The study of enzymes is called ''enzymology'' and the field of pseudoenzyme, pseudoenzyme analysis recognizes that during evolution, some enzymes have lost the ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual 'pseudocatalytic' properties. Enzymes are known to catalyze more than 5,000 biochemical reaction types. Other biocatalysts include Ribozyme, catalytic RNA molecules, also called ribozymes. They are sometimes descr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pribnow Box
The Pribnow box (also known as the Pribnow-Schaller box) is a sequence of ''TATAAT'' of six nucleotides (thymine, adenine, thymine, etc.) that is an essential part of a promoter site on DNA for transcription to occur in bacteria. It is an idealized or consensus sequence—that is, it shows the most frequently occurring base at each position in many promoters analyzed; individual promoters often vary from the consensus at one or more positions. It is also commonly called the -10 sequence or element, because it is centered roughly ten base pairs upstream from the site of initiation of transcription. The Pribnow box has a function similar to the TATA box that occurs in promoters in eukaryotes and archaea: it is recognized and bound by a subunit of RNA polymerase during initiation of transcription. This region of the DNA is also the first place where base pairs separate during prokaryotic transcription to allow access to the template strand. The AT-richness is important to allo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sigma 70 Domains
Sigma ( ; uppercase Σ, lowercase σ, lowercase in word-final position ς; ) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used as an operator for summation. When used at the end of a letter-case word (one that does not use all caps), the final form (ς) is used. In ' (Odysseus), for example, the two lowercase sigmas (σ) in the center of the name are distinct from the word-final sigma (ς) at the end. The Latin letter S derives from sigma while the Cyrillic letter Es derives from a lunate form of this letter. History The shape (Σς) and alphabetic position of sigma is derived from the Phoenician letter ( ''shin''). Sigma's original name may have been ''san'', but due to the complicated early history of the Greek epichoric alphabets, ''san'' came to be identified as a separate letter in the Greek alphabet, represented as Ϻ. Herodotus reports that "san" was the name gi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anti-sigma Factors
Introduction Anti-sigma factors are small proteins that bind to sigma factors and inhibit transcriptional activity in regulating prokaryote gene expression. Anti-sigma factors have both a sigma-binding domain and a sensory/signaling domain; this allows them to respond to signals inside and outside the cell. Anti-sigma factors have been found in several bacteria, including ''Escherichia coli'' and ''Salmonella'', and viruses such as the T4 bacteriophage. Anti-sigma factors have an antagonistic effect on sigma factors. Each sigma factor has an associated anti-sigma factor that regulates it. These anti-sigma factors are divided into cytoplasmic-bound anti-sigma factors and inner membrane-bound anti-sigma factors. The differences in these sigma factors are where in the cell they are bound. Cytoplasmic-bound anti-sigma factors include FlgM, DnaK, RssB, and HscC. Inner membrane-bound anti-sigma factors, also called extra-cytoplasmic function (ECF) anti-sigma factors, include FecR and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RpoN
The gene ''rpoN'' (RNA polymerase, nitrogen-limitation N) encodes the sigma factor ''sigma-54'' (σ54, sigma N, or RpoN), a protein in ''Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...'' and other species of bacteria. RpoN antagonizes RpoS sigma factors. Biological role Originally identified as a regulator of genes involved in nitrogen metabolism and assimilation under nitrogen limiting conditions, ''E. coli'' σ54 has since been shown to play important regulatory roles in a variety of other cellular processes. Similarly, σ54 homologues in other species regulate a wide range of processes, including flagellar synthesis and virulence. Sequence specificity and mechanism of action σ54 promoter elements consist of conserved nucleotides located at −12 and −2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RpoS
The gene ''rpoS'' (RNA polymerase, sigma S, also called katF) encodes the sigma factor ''sigma-38'' (σ38, or RpoS), a 37.8 kD protein in ''Escherichia coli''. Sigma factors are proteins that regulate transcription (genetics), transcription in bacteria. Sigma factors can be activated in response to different environmental conditions. ''rpoS'' is transcribed in late exponential phase, and RpoS is the primary regulator of stationary phase genes. RpoS is a central regulator of the general stress response and operates in both a retroactive and a proactive manner: it not only allows the cell to survive environmental challenges, but it also prepares the cell for subsequent stresses (cross-protection). The transcriptional regulator CsgD is central to biofilm formation, controlling the expression of the curli structural and export proteins, and the diguanylate cyclase, adrA, which indirectly activates cellulose production. The ''rpoS'' gene most likely originated in the gammaproteobacte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proteases
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products. They do this by cleaving the peptide bonds within proteins by hydrolysis, a reaction where water breaks bonds. Proteases are involved in numerous biological pathways, including digestion of ingested proteins, protein catabolism (breakdown of old proteins), and cell signaling. In the absence of functional accelerants, proteolysis would be very slow, taking hundreds of years. Proteases can be found in all forms of life and viruses. They have independently evolved multiple times, and different classes of protease can perform the same reaction by completely different catalytic mechanisms. Classification Based on catalytic residue Proteases can be classified into seven broad groups: * Serine proteases - using a serine alcohol * Cysteine prot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chaperone (protein)
In molecular biology, molecular chaperones are proteins that assist the conformational folding or unfolding of large proteins or macromolecular protein complexes. There are a number of classes of molecular chaperones, all of which function to assist large proteins in proper protein folding during or after synthesis, and after partial denaturation. Chaperones are also involved in the translocation of proteins for proteolysis. The first molecular chaperones discovered were a type of assembly chaperones which assist in the assembly of nucleosomes from folded histones and DNA. One major function of molecular chaperones is to prevent the aggregation of misfolded proteins, thus many chaperone proteins are classified as heat shock proteins, as the tendency for protein aggregation is increased by heat stress. The majority of molecular chaperones do not convey any steric information for protein folding, and instead assist in protein folding by binding to and stabilizing folding intermedi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heat Shock Response
The heat shock response (HSR) is a cell stress response that increases the number of molecular chaperones to combat the negative effects on proteins caused by stressors such as increased temperatures, oxidative stress, and heavy metals. In a normal cell, proteostasis (protein homeostasis) must be maintained because proteins are the main functional units of the cell. Many proteins take on a defined configuration in a process known as protein folding in order to perform their biological functions. If these structures are altered, critical processes could be affected, leading to cell damage or death. The heat shock response can be employed under stress to induce the expression of heat shock proteins (HSP), many of which are molecular chaperones, that help prevent or reverse protein misfolding and provide an environment for proper folding. Protein folding is already challenging due to the crowded intracellular space where aberrant interactions can arise; it becomes more difficult whe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
