We have identified a serum-inducible gene, relB, which encodes a protein of 558 amino acids containing a region with high similarity to c-Rel and other members of the Rel family. Transcriptional activation analysis of GAL4-RelB fusion proteins in yeast cells reveals that RelB contains in its C-terminal 180 amino acids a transcriptional activation domain. The N-terminal part including the region of similarity with the Rel family shows no detectable transcriptional activity. RelB does not bind with high affinity to NF-KB sites, but heterodimers between RelB and p50-NF-KB do bind to different NF-KtB-binding sites with a similar affinity to that shown by p50-NF-KB homodimers. However, RelB/p50-NF-KB heterodimers, in contrast to p50-NF-KB homodimers, transactivate transcription of a promoter containing a KB-binding site.Growth factors and other mitogens are capable of rapidly inducing a complex set of more than 100 genes in quiescent fibroblasts (1,13,31,32,38). These genes, which have been named immediate-early or early response genes, are transcriptionally activated within minutes after addition of growth factor or mitogen independently of de novo protein synthesis. Among these genes are several encoding bona fide or putative transcription factors such as members of the fos and jun families, zinc finger proteins (for reviews, see references 8, 22, and 33), or others containing undefined motifs like the Rel domain found in the proto-oncogene c-rel product (11,12,20) and the transcription factor NF-KB (7,16,28,44,47,49,51).The proto-oncogene c-rel (60) is the cellular homolog of the v-rel oncogene (53), isolated from reticuloendotheliosis virus strain T, a turkey-derived acutely transforming retrovirus (56) causing lymphoid leukemia. The c-rellv-rel genes are part of a rapidly growing family of transcription factors. One member of this family is the dorsal gene of Drosophila melanogaster, which is involved in establishing the dorsalventral axis (54) and is able to bind to NF-KB-like DNA sequences (23, 57). The other members are the transcription factor p50-NF-KB (also known as KBF1) with its precursor pl05-NF-KB (7,16,28,44), p50B(p49)-NF-KB with its precursor p97-NF-KB (6a, 51), and p65-NF-KB (47, 49). p50 and p65 form a heterodimer that is able to bind to NF-KB-binding sites found in many enhancers and promoters such as in the immunoglobulin kappa genes, interleukin-2, interleukin-6, ,-interferon, and others (for a review, see reference 35).All the members of the Rel family share a highly conserved domain of approximately 300 amino acids termed the Rel domain, which is considered to function as a DNAbinding and protein dimerization region with properties yet to be defined in detail. Additionally, all the members of this family show a regulated movement from the cytoplasm to the nucleus (for reviews, see references 17 and 36). In particular for the NF-KB complex it is known that p65 is able * Corresponding author.to interact with an inhibitor, IKB, which keeps it in the cytoplasm. After activation of cells, IKB is i...

We have shown that the murine c-rel protein can act as a transcriptional transactivator in both yeast and mammalian cells. Fusion proteins generated by linking rel sequences to the DNA-binding domain of the yeast trascriptional activator GAL4 activate transcription from a reporter gene linked in cis to a GAL4 binding site. The full-length mouse c-rel protein (588 amino acids long) is a poor transactivator; however, the C-terminal portion of the protein between amino acid residues 403 to 568 is a potent transcriptional transactivator. Deletion of the N-terminal half of the c-rel protein augments its transactivation function. We propose that c-rel protein has an N-terminal regulatory domain and a C-terminal transactivation domain which together modulate its function as a transcriptional transactivator.The immediate cellular response to external stimulus culminates in the induction of a large set of nuclear genes. Some of these early response genes are proto-oncogenes, and their products have been shown to be involved in the transcription of other genes (1,9,13,17,32,33,41,42). The theme of oncogenes as transcriptional factors or cofactors has been well illustrated by the Fos-Jun paradigm (13). The two nuclear oncoproteins associate to form heterodimers which bind to their cognate DNA motif to promote transactivation (12, 50). More recently, the product of the protooncogene myb has also been shown to act as a transcriptional activator (42, 62). Interestingly, the BAS1 protein, which is required for activation of GCN4-independent (basal) HIS4 transcription in yeast, shares homology to the N-terminal region of myb protein (58). The c-rel gene is a member of the immediate-early response gene family and is induced by serum and phorbol ester (TPA) (9). Its viral homolog, the v-rel protein, has been shown to function as a transcriptional activator in certain cell types (20,25).v-rel is the resident transforming gene of reticuloendotheliosis virus strain T, a highly oncogenic avian retrovirus that induces a rapidly fatal lymphoma in young birds (18,57). Reticuloendotheliosis virus strain transforms only avian lymphoid cells, and despite high levels of expression in chicken embryo fibroblasts, no transformed phenotype is evident (10,23,54). The product of v-rel is a 59-kilodalton phosphoprotein that is located in the cytoplasm of transformed spleen cells and in the nucleus of the nontransformed fibroblasts (10,19,22,54). However, subcellular localization appears to be irrelevant, because both cytoplasmic and nuclear forms of the v-rel protein can induce cellular transformation (23, 25). The v-rel protein has been shown to associate with a number of cellular proteins, including a closely associated serine-threonine protein kinase in both untransformed chicken embryo fibroblasts and transformed spleen cells (15,53,60 whereas in mouse and human cells it is 7.5 and 10 kilobases, respectively (8)(9)(10)26). Although c-rel expression is seen in many cell types, high levels are observed only in lymphoid cells (6,8).The c-rel prot...

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The P2X 7 receptor is a non-selective cationic channel activated by extracellular ATP, belonging to the P2X receptor family. To assess the role of extracellular histidines on the allosteric modulation of the rat P2X 7 receptor by divalent metals (copper, zinc and magnesium) and protons, these amino acid residues were singly substituted for corresponding alanines. Wild-type and mutated receptors were injected to Xenopus laevis oocytes; metal-related effects were evaluated by the two-electrode voltage-clamp technique. Copper inhibited the ATP-gated currents with a median inhibitory concentration of 4.4 ± 1.0 lmol/L. The inhibition was noncompetitive and time-dependent; copper was 60-fold more potent than zinc. The mutant H267A, resulted in a copper resistant receptor; mutants H201A and H130A were less sensitive to copper inhibition (p < 0.05). The rest of the mutants examined, H62A, H85A, and H219A, conserved the copper-induced inhibition. Only mutants H267A and H219Awere less sensitive to the modulator action of zinc. Moreover, the magnesium-induced inhibition was abolished exclusively on the H130A and H201A mutants, suggesting that this metal may act at a novel cationic modulator site. Media acidification inhibited the ATP-gated current 87 ± 3%; out of the six mutants examined, only H130A was significantly less sensitive to the change in pH, suggesting that His-130 could be involved as a pH sensor. In conclusion, while His-267 is critically involved in the copper or zinc allosteric modulation, the magnesium inhibitory effects is related to His-130 and His-201, His-130 is involved in proton sensing, highlighting the role of defined extracellular histidines in rat P2X 7 receptor allosteric modulation.