RelB is a component of the NF-kappa-B RelB-p50 complex and the RelB-p52 complex []. It is best known for its roles in lymphoid development and noncanonical signalling [], but it seems to be linked to many distinct processes. Among others, RelB may have a role in suppressing inflammation []and has been shown to negatively regulate osteoblast differentiation and bone formation [].NF-kappaB is a pleiotropic transcription factor present in almost all cell types. It is the endpoint of a series of signal transduction events that are initiated by a vast array of stimuli related to many biological processes such as inflammation, immunity, differentiation, cell growth, tumorigenesis and apoptosis. NF-kappaB is a homo- or heterodimeric complex formed by the Rel-like domain-containing proteins RelA/p65, RelB, NFKB1/p50, c-Rel and NFKB2/p52 []. Each individual NF-kappaB subunit, and perhaps each dimer, carries out unique functions in regulating transcription. Dimer-specific functions can be conferred by selective protein-protein interactions with other transcription factors, coregulatory proteins, and chromatin proteins [].
Plasmids may be maintained stably in bacterial populations through the action of addiction modules, in which a toxin and antidote are encoded in a cassette on the plasmid. In any daughter cell that lacks the plasmid, the toxin persists and is lethal after the antidote protein is depleted. Toxin/antitoxin pairs are also found on main chromosomes, and likely represent selfish DNA. Sequences in the seed for this alignment all were found adjacent to toxin genes. Several toxin/antitoxin pairs may occur in a single species. RelE and RelB form a toxin-antitoxin system; RelE cleaves mRNA during translation on the ribosome [, , ]. RelB binds and inhibits RelE and it regulates transcription by operator binding and conditional cooperativity controlled by RelE. RelE and RelB form a V-shaped heterotetrameric complex which has a ribbon-helix-helix (RHH) dimerization domain at the apex. [].DinJ is an antitoxin component of a toxin-antitoxin (TA) module. It is a labile antitoxin that counteracts the effect of the YafQ toxin []. It forms a heterotetrameric complex with YafQ and the structure of this complex revealed that the N-terminal region of DinJ folds into a ribbon-helix-helix motif that dimerises for DNA recognition, and the C-terminal portion of each DinJ wraps around a YafQ molecule []. Together, they they bind their own promoter, and by analogy to other TA modules probably repress its expression. Cell death governed by the mazEF and dinJ-yafQ TA modules seems to play a role in biofilm formation [, , ].
This family represents the RelB antitoxin of toxin-antitoxin stability system or prevent-host death system. Together RelE toxin and the RelB antitoxin form a non-toxic complex. Although toxin-antitoxin gene cassettes were first found in plasmids, it is clear that these loci are abundant in free-living prokaryotes, including many pathogenic bacteria, and these toxin-antitoxin loci provide a control mechanism that helps free-living prokaryotes cope with nutritional stress [, ].
The transcription factor NF-kB (Nuclear Factor-kappaB) was first identified as a DNA-binding protein specific for the 10-base pair kB site in the immunoglobulin k light-chain enhancer of B lymphocytes [], but has subsequently been found in many different cell types. NF-kB represents a group of structurally related proteins that share a 300 amino acid `Rel homology domain' (RHD) []: members include p50 (NF-kB1), p52 (NF-kB2), p65 (RelA), c-Rel, v-Rrel, RelB, and the Drosophila proteins Dorsal and Dif. These proteins exist as homo- and heterodimers that bind to kB sites in the enhancer regions of several target genes, most of which are involved in cellular defence mechanisms and differentiation.The RHD, which is located N-terminally, is responsible for proteindimerisation, DNA binding and nuclear localisation. The more variableC-terminal transactivation domain is found in RelA, RelB and c-Rel, but not in p50 or p52. Nevertheless, p50 and p52 play critical roles in modulatingthe specificity of NF-kB function. DNA binding requires the entire RHD, by contrast with other eukaryotic and prokaryotic transcription factors, where muchsmaller DNA-binding domains confer full specificity and bindingaffinity for the target []. The structure of the transcription factor NF-kB p50 homodimer bound to a palindromic kB site shows the RHD to fold into 2 distinct subdomains, similar to the β-sandwich structure of the immunoglobulins [].NF-kB is expressed in the cytoplasm of virtually all cell types, where its activity is controlled by a family of regulatory proteins, called inhibitors of NF-kB (IkB) [, ].
This entry represents the NF-kappaB subunit precursor p100, which can be processed to produce a 52kDa protein (p52). p52 can form homodimers. It can also form heterodimers with different NF-kappaB family members, such as RelB, p65 and c-Rel [, ]. p100 inhibits c-Rel and reduces the expression of IL-23 in dendritic cells [].NF-kappaB is a pleiotropic transcription factor present in almost all cell types. It is the endpoint of a series of signal transduction events that are initiated by a vast array of stimuli related to many biological processes such as inflammation, immunity, differentiation, cell growth, tumorigenesis and apoptosis. NF-kappaB is a homo- or heterodimeric complex formed by the Rel-like domain-containing proteins RelA/p65, RelB, NFKB1/p50, c-Rel and NFKB2/p52 []. Each individual NF-kappaB subunit, and perhaps each dimer, carries out unique functions in regulating transcription. Dimer-specific functions can be conferred by selective protein-protein interactions with other transcription factors, coregulatory proteins, and chromatin proteins [].NF-kB1 and NF-kB2 are synthesised as large precursors, called p105 and p100, which undergo processing to generate the NF-kB subunits p50 and p52, respectively []. The processing of p105 and p100 is mediated by the ubiquitin/proteasome pathway, and involves selective degradation of their C-terminal regions containing ankyrin repeats []. Unlike RelA, RelB and c-Rel, p50 and p52 do not contain transactivation domains in their C-termini. Nevertheless, they play critical roles in modulating the specificity of NF-kB function [].
This entry represents the NF-kappaB subunit precursor p105, which can undergo cotranslational processing by the 26S proteasome to produce a 50kDa protein (p50). p50 is a DNA binding subunit of the NF-kappaB (NF-kappaB) protein complex [].NF-kappaB is a pleiotropic transcription factor present in almost all cell types. It is the endpoint of a series of signal transduction events that are initiated by a vast array of stimuli related to many biological processes such as inflammation, immunity, differentiation, cell growth, tumorigenesis and apoptosis. NF-kappaB is a homo- or heterodimeric complex formed by the Rel-like domain-containing proteins RelA/p65, RelB, NFKB1/p50, c-Rel and NFKB2/p52 []. Each individual NF-kappaB subunit, and perhaps each dimer, carries out unique functions in regulating transcription. Dimer-specific functions can be conferred by selective protein-protein interactions with other transcription factors, coregulatory proteins, and chromatin proteins [].NF-kB1 and NF-kB2 are synthesised as large precursors, called p105 and p100, which undergo processing to generate the NF-kB subunits p50 and p52, respectively []. The processing of p105 and p100 is mediated by the ubiquitin/proteasome pathway, and involves selective degradation of their C-terminal regions containing ankyrin repeats []. Unlike RelA, RelB and c-Rel, p50 and p52 do not contain transactivation domains in their C-termini. Nevertheless, they play critical roles in modulating the specificity of NF-kB function [].
