The NF-B pathway plays a critical role in regulating cellular processes such as immune responses, stress responses, apoptosis, proliferation and differentiation, whereas dysfunction of this pathway has been associated with numerous cancer and immune disorders. We have applied our Random Activation of Gene Expression technology to an NF-B reporter cell line to facilitate the discovery of positive regulators of NF-B activation. A small protein expression library, corresponding to Ϸ0.1؋ genome coverage, was generated and screened for clones exhibiting constitutive activation of NF-B. After isolation of cellular clones displaying the relevant phenotypes, we identified two known components of the NF-B pathway and a hypothetical gene that we have designated the human ortholog of Xenopus TAK1-binding protein 3 (TAB3). Overexpression of human TAB3 was found to activate both NF-B and AP-1 transcription factors. Furthermore, the activation of NF-B by TAB3 was blocked by the NF-B inhibitor, SN50, and by expression of dominant-negative forms of tumor necrosis factor ␣-associated factor 6 and transforming growth factor -activated kinase. Taken together, these data demonstrate that TAB3 transforming growth factor is a constituent of the NF-B pathway functioning upstream of tumor necrosis factor ␣-associated factor 6͞transforming growth factor -activated kinase. Interestingly, increased expression of TAB3 was found in some cancer tissues, and its overexpression in NIH 3T3 cells resulted in cellular transformation, thus establishing a causative link between elevated TAB3 expression, constitutive NF-B activation, and oncogenesis.
A 6-kilobase-pair (kbp) region of the genome of the extremely thermophilic archaebacterium Methanothermusfervidus which encodes the a, ,1, and y subunit polypeptides of component C of methyl coenzyme M reductase was cloned and sequenced. Genes encoding the (mcrB) and -y (merG) subunits were separated by two open reading frames (designated mcrC and mcrD) which encode unknown gene products. The M. fervidus genes were preceded by ribosome-binding sites, separated by short A+T-rich intergenic regions, contained unexpectedly few NNC codons, and exhibited inflexible codon usage at some locations. Sites of transcription initiation and termination flanking the mcrBDCGA cluster of genes in M. fervidus were identified. The sequences of the genes, the encoded polypeptides, and transcription regulatory signals in M. fervidus were compared with the functionally equivalent sequences from two mesophilic methanogens (Methanococcus vannielii and Methanosarcina barkeri) and from a moderate thermophile (Methanobacterium thermoautotrophicum Marburg). The amino acid sequences of the polypeptides encoded by the mcrBCGA genes in the two thermophiles were approximately 80% identical, whereas all other pairs of these gene products contained between 50 and 60% identical amino acid residues. The mcrD gene products have diverged more than the products of the other mcr genes. Identification of highly conserved regions within mcrA and mcrB suggested oligonucleotide sequences which might be developed as hybridization probes which could be used for identifying and quantifying all methanogens.Methanogens constitute an extremely diverse group of archaebacteria with genomes which range from 28 to 61 mol% G+C. There are bacillary, coccal, and spiral methanogens, and their habitats are as different as the human gut and volcanic vents. Their ability to synthesize methane is, however, a unifying feature, and the terminal reaction in methanogenesis, reduction of a methyl group bound to coenzyme M, is common to all methanogens (2, 12, 33). The enzyme which catalyzes this reaction, component C of methyl coenzyme M reductase (methyl reductase), has been purified from several methanogens and found in all cases to contain three different subunit polypeptides, designated ox, 1, and -y (8,11,14,18). Conservation in the structure and function of methyl reductases has been shown by immunological cross-reactivities and methanogenesis in vitro with reaction mixtures containing components prepared from different methanogens (11). Cloning and sequencing of the genes encoding the ox, 1, and -y subunits of methyl-coenzyme M reductase (mcrA, mcrB, and mcrG, respectively) from Methanococcus vannielii, Methanosarcina barkeri, and Methanobacterium thermoautotrophicum has recently been reported (4-6), and we have now extended this work to Methanothermus fervidus, a very unusual methanogen, isolated from a volcanic hot spring, with an optimum growth temperature of 83°C (25 ously reported from the two mesophiles (M. vannielii and M. barkeri) and the moderate thermophile (M...
Peroxidases constitute an enzyme family that displays tremendous diversity in form, function and distribution throughout the plant kingdom [ 1 I.Kecent studies on certain cell wall-associated anionic peroxidases strongly suggest that they are involved in cell wall fortification for defence purposes [Z, 31. In this paper we will confine our discussion to these recent findings. Cell wall-associated phenolicsOne of the important functions of anionic peroxidases is to catalyse cross-linking and polymerization of cell wall-associated phenolic polymers [4].
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