Anionic amphiphile-independent activation of the phagocyte NADPH oxidase in a cell-free system by p47phox and p67phox, both in C terminally truncated forms. Implication for regulatory Src homology 3 domain-mediated interactions

Anionic amphiphiles, such as arachidonate, activate the superoxide-producing phagocyte NADPH oxidase in a cell-free system with human neutrophil membrane, which contains cytochrome b558 comprising gp91(phox) and p22(phox), and three cytosolic proteins: p47(phox) and p67(phox), each harboring two SH3 domains, and the small GTPase Rac. Here we show that, even without the amphiphiles, the oxidase is activated in vitro by a C terminally truncated p47(phox), retaining the N-terminal and the two SH3 domains, and the N terminus of p67(phox). When either truncated p47(phox) or p67(phox) is replaced by the respective full-length one, the activation absolutely requires the amphiphiles. The results indicate that both p47(phox) and p67(phox) are the primary targets of the amphiphiles, and that their C-terminal regions play negative regulatory roles. We also find that the truncated p47(phox), but not the full-length one, can bind to p22(phox), a binding required for the oxidase activation. The N-terminal SH3 domain of p47(phox) is responsible for the binding not only to p22(phox), but also to the p47(phox) C terminus. Thus the SH3 domain is accessible in the active p47(phox), but is normally masked in the full-length one probably via intramolecularly interacting with the C terminus. The present findings support our previous proposal of regulatory SH3 domain-mediated interactions.

Functional modules and expression of mouse p40(phox) and p67(phox), SH3-domain-containing proteins involved in the phagocyte NADPH oxidase complex

The phagocyte NADPH oxidase is activated during phagocytosis to produce superoxide, a precursor of microbicidal oxidants. The formation of the active oxidase complex at the membrane requires translocation of the Rac GTPase and two specialized cytosolic proteins that harbor SH3 domains, p67phox and p47phox. Another SH3-domain-containing protein p40phox, which is constitutively associated with p67phox in phagocytes, also enters the complex upon cell stimulation. Here we describe how we cloned mouse cDNAs encoding p40phox and its partner in phagocytes, p67phox. Both p40phox and p67phox comprise several protein-binding modules that are structurally and functionally well conserved between mouse and human, indicating their nature as adaptor proteins. We have also systematically investigated expression of the gene for p40phox in comparison with those for p67phox and p47phox. Distributions of the mRNAs for the three proteins among tissues are similar, with the most abundant expression in the spleen. The messages are abundant not only in phagocytic cells, but also in B cell lineage. The p40phox gene, but not the other two, is expressed in some types of cells such as plasma cells and T lymphocytes. Furthermore, in situ hybridization analysis shows that the p40phox mRNA is distributed in neuronal cells of mouse brain, providing evidence that one of the genes for the specialized oxidase factors is expressed in neurons. These observations raise the possibility that the adaptor protein p40phox plays a heretofore unsuspected role via interacting with other proteins in the cells that do not express p67phox or p47phox.

The PC motif: a novel and evolutionarily conserved sequence involved in interaction between p40phox and p67phox, SH3 domain-containing cytosolic factors of the phagocyte NADPH oxidase

The superoxide-generating NADPH oxidase, dormant in resting phagocytes, is activated during phagocytosis following assembly of the membrane-integrated protein cytochrome b558 and cytosolic factors. Among the latter are the three proteins containing Src homology 3 (SH3) domains, p67phox, p47phox and p40phox. While the first two factors are indispensable for the activity, p40phox is tightly associated with p67phox in resting cells and is suggested to have some modulatory role. Here we describe a systematic analysis of the interaction between p40phox and p67phox using the yeast two-hybrid system and in vitro binding assays with recombinant proteins. Both methods unequivocally showed that the minimum requirements for stable interaction are the C-terminal region of p40phox and the region between the two SH3 domains of p67phox. This interaction is maintained even in the presence of anionic amphiphiles used for the activation of the NADPH oxidase, raising a possibility that it mediates constitutive association of the two factors in both resting and activated cells. The C-terminal region of p40phox responsible for the interaction contains a characteristic stretch of amino acids designated as the PC motif, that also exists in other signal-transducing proteins from yeast to human. Intensive site-directed mutagenesis to the motif in p40phox revealed that it plays a critical role in the binding to p67phox. Thus the PC motif appears to represent a novel module for protein-protein interaction used in a variety of signaling pathways.

Superiority of interleukin-12-transduced murine lung cancer cells to GM-CSF or B7-1 (CD80) transfectants for therapeutic antitumor immunity in syngeneic immunocompetent mice

Interleukin-12 (IL-12) is a heterodimeric cytokine that consists of p40 and p35 subunits. IL-12 has been regarded as a potent inducer of host antitumor immunity through interferon-gamma (IFN-gamma) production and development of Th1 helper T cells from Th0 cells. Here, we demonstrate the immunomodulatory actions of an IL-12-transduced murine lung cancer cell line, Lewis lung carcinoma (LLC) (LLC/IL12) cells, in syngeneic C57BL/6 mice. We also report on their therapeutic potency. Three LLC/IL12 cells producing different levels of IL-12 were cloned and found to have diminished tumorigenicity in C57BL/6 mice depending on their level of IL-12 production. In vivo depletion assay demonstrated that the loss of tumorigenicity of LLC/IL12 depended on both CD4+ and CD8+ T cells, and that natural killer (NK) cells were involved, especially in the early phase of immunity. The strong systemic antitumor immunity against challenge with wild type LLC (LLC/wt) cells was also induced by LLC/IL12 cells. The systemic antitumor memory was found to be dependent mainly on the CD4+ T-cell subset. 51Cr-release assay revealed that the killer activity consisted of a specific killer activity directed at the parental LLC/wt cells and a nonspecific killer activity directed at both LLC/wt and syngeneic EL-4 thymoma cells. In addition, LLC/IL12 apparently had a much stronger antitumor effect against the established LLC/wt tumor than LLC transduced with B7-1 or GM-CSF cDNA. IL-12 can be considered an efficient candidate molecule for immunogene therapy for lung cancer in this experimental system.

Roles for proline-rich regions of p47phox and p67phox in the phagocyte NADPH oxidase activation in vitro

The cytosolic proteins p47phox and p67phox, each containing two SH3 domains, are required for activation of the superoxide-producing phagocyte NADPH oxidase in a cell-free system with human neutrophil membrane and the small GTPase Rac. Here we focus on roles of proline-rich regions (PRRs) that reside in p47phox and p67phox. Deletion of the p47phox PRR, to which the C-terminal SH3 domain of p67phox binds, results in three-fold decreased activation of the enzyme in the cell-free system with the full-length p67phox, suggesting a modulatory role of the p47phox PRR. The modulation is likely mediated via the C-terminal region of p67phox, since the p47phox mutant protein fully activates the oxidase in combination with the N-terminus of p67phox. Neither deletion of the p67phox PRR nor substitutions for prolines in the region affects the ability to support superoxide production under the cell-free conditions, indicating that the PRR of p67phox has no primary function in the oxidase activation.

GM-CSF and B7-1 (CD80) co-stimulatory signals co-operate in the induction of effective anti-tumor immunity in syngeneic mice

B7-1 (CD80) co-stimulatory molecule gene-transduced Lewis lung carcinoma (LLC) cells (LLC/B7 cells) resulted in remarkable loss of tumorigenicity in syngeneic C57BL/6 mice (87.5% rejection) compared to B7-negative, wild-type LLC (LLC/wt) cells (0% rejection). However, mice that had rejected LLC/B7 cells developed almost no systemic immunity protective against challenge with wild-type tumor cells after 4 weeks (11.8% rejection). Enhancement of MHC class I (H-2Kb) expression of LLC/B7 cells with in vitro interferon-gamma treatment did not result in enhancement of protective immunity. In vivo depletion assay revealed that abrogation of tumorigenicity in LLC/B7 depended on CD8+ T cells but not on CD4+ T cells. However, vaccination of C57BL/6 mice with irradiated LLC cells transduced with GM-CSF (LLC/GM) led to the induction of potent, specific immunity against challenge with the LLC/wt cells after 2 weeks (80.8% rejection). Next, we established a double transfectant of LLC cells expressing both B7-1 and GM-CSF (LLC/GM + B7). The tumorigenicity of these clonal cells was also remarkably suppressed (90% rejection) to the same degree as LLC/B7, whereas that of LLC/GM was not suppressed (0% rejection). Interestingly, mice that had rejected LLC/GM+B7 cells developed enhanced protective immunity against challenge with LLC/wt cells after 4 weeks (55.6% rejection) compared to the results of LLC/B7 cells (11.8%). To evaluate whether co-expression of GM-CSF and B7-1 enabled the tumor cells to activate cytotoxic T cells more efficiently than B7-1 alone, we performed an in vitro killing assay. We found that immunization with LLC/GM+B7 cells resulted in a 3-fold stronger cytotoxic response than that with LLC/B7. Our data indicate that co-transfection of the B7-1 co-stimulatory molecule and GM-CSF genes may be more effective for the induction of stronger protective immunity in this experimental system.

Two novel mutations in the reduced nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase gene of a patient with generalized type, hereditary methemoglobinemia

Hereditary methemoglobinemia due to reduced nicotinamide adenine dinucleotide (NADH) cytochrome b5 reductase (b5R) deficiency is classified into two types, an erythrocyte (type I) and a generalized (type II). We investigated the b5R gene of a patient with type II from a white United Kingdom (UK) family and found that the patient was a compound heterozygote for two novel mutations. The first mutation was a C-to-A transversion changing codon 42 (TAC: Tyr) to a stop codon in the one allele. From this mutant allele, the product without the catalytic portion of the enzyme is generated. The second one was a missense mutation at codon 95 (CCC-->CAC) in the other allele with the result that Pro changed to His within the flavin adenine dinucleotide (FAD)-binding domain of the enzyme. To characterize effects of this missense mutation on the enzyme function, we compared glutathione S-transferase (GST)-fused b5R with the GST-fused mutant enzyme with the codon 95 missense mutation (P95H) expressed in Escherichia coll. The mutant enzyme showed less catalytic activity, less thermostability, and a greater susceptibility to trypsin than did the normal counterpart. The absorption spectrum of the mutant enzyme in the visual region differed from that of the wild-type. These results suggest that this amino acid substitution influences both secondary structure and catalytic activity of the enzyme. The compound heterozygosity for the nonsense and the missense mutations apparently caused hereditary methemoglobinemia type II in this patient.

Assembly and activation of the phagocyte NADPH oxidase. Specific interaction of the N-terminal Src homology 3 domain of p47phox with p22phox is required for activation of the NADPH oxidase

The phagocyte NADPH oxidase is activated during phagocytosis to produce superoxide, a precursor of microbicidal oxidants. The activation involves assembly of membrane-integrated cytochrome b558 comprising gp91(phox) and p22(phox), two specialized cytosolic proteins (p47(phox) and p67(phox)), each containing two Src homology 3 (SH3) domains, and the small G protein Rac. In the present study, we show that the N-terminal SH3 domain of p47(phox) binds to the C-terminal cytoplasmic tail of p22(phox) with high affinity (KD = 0.34 microM). The binding is specific to this domain among several SH3 domains including the C-terminal one of p47(phox) and the two of p67(phox) and requires the Pro156-containing proline-rich sequence but not other putative SH3 domain-binding sites of p22(phox). Replacement of Trp193 by Arg in the N-terminal SH3 domain completely abrogates the association with p22(phox). A mutant p47(phox) with this substitution is incapable of supporting superoxide production under cell-free activation conditions. These findings provide direct evidence that the interaction between the N-terminal SH3 domain of p47(phox) and the proline-rich region of p22(phox) is essential for activation of the NADPH oxidase.

An SH3 domain-mediated interaction between the phagocyte NADPH oxidase factors p40phox and p47phox

The phagocyte NADPH oxidase is activated during phagocytosis to produce superoxide, following assembly of a membrane-integrated cytochrome b558 with cytosolic proteins, p47phox, p67phox and p40phox, each containing Src homology 3 (SH3) domains. While both p47phox and p67phox are indispensable for the oxidase activity, role of p40phox remains obscure. Here we study interaction between p40phox and p47phox by two independent methods, a two-hybrid system in the yeast and an in vitro binding assay using purified proteins. The present results show that the interaction is mediated via binding of the SH3 domain of p40phox to a C-terminal proline-rich region of p47phox. This proline-rich region is also the target for binding of p67phox, and the SH3 domain of p40phox can inhibit the binding of the C-terminal one of p67phox to p47phox.

Effects of L-arginine analogues on vasomotion of isolated porcine coronary arteries

L-Arginine analogues have been widely used to examine the role of endothelium-derived nitric oxide (NO) in vascular responses; however, the effects of the agents on coronary vasomotion are not fully understood. In this study, we examined the effects of the analogues on vasomotion of isolated porcine coronary arteries. Strips of the porcine coronary artery were suspended for isometric tension recording in Krebs-Henseleit solution. L-Arginine analogues, N omega-nitro-L-arginine methyl ester (L-NAME, 10(-9)-10(-3) M), NG-monomethyl-L-arginine (L-NMMA, 10(-9)-10(-3) M), and NG-nitro-L-arginine (L-NNA, 10(-9)-10(-3) M), caused dose-dependent contractions, which were greater in strips with than in those without endothelium. Those endothelium-dependent contractions were almost abolished by indomethacin (10(-5) M) and FeCl2 (10(-3) M). The latter reduces prostaglandin H2 to 12-heptadecatrienoic acid, which has no vasoconstrictor effect. These results indicate that the L-arginine analogues cause endothelium-dependent contractions that are mediated by prostaglandin endoperoxides and suggest that they have properties other than simple inhibition of NO synthesis in porcine coronary arteries.

omega-Oxidation of lipoxin B4 by rat liver. Identification of an omega-carboxy metabolite of lipoxin B4

Lipoxin B4 (LXB4) is metabolized to 20-hydroxy-LXB4 by rat liver microsomes. The omega-hydroxylation requires both molecular oxygen and NADPH, and is inhibited by carbon monoxide, indicating involvement of a cytochrome P-450 (P-450). This is supported by inhibition of the reaction by antibodies raised against NADPH-P-450 reductase. The P-450 appears to be the one responsible for leukotriene B4 omega-hydroxylation, because leukotriene B4 inhibits the formation of 20-hydroxy-LXB4 and LXB4 blocks the leukotriene B4 omega-hydroxylase activity in microsomes. Incubation of 20-hydroxy-LXB4 with both rat liver cytosol and NAD+ leads to formation of a more polar metabolite on high-performance liquid chromatography. The metabolite is identified as 20-carboxy-LXB4, a novel metabolite of LXB4, based on analyses by ultraviolet spectrometry and by gas chromatography/mass spectrometry. The 20-carboxy-LXB4-forming activity is localized in cytosol, with an optimal pH of 8.5. The activity is dependent on NAD+, but NADP+ can not replace NAD+. The reaction is inhibited by pyrazole and 4-methylpyrazole, inhibitors of alcohol dehydrogenase, and by substrates of the enzyme such as ethanol and 20-hydroxy-leukotriene B4. Disulfiram, an inhibitor of aldehyde dehydrogenase, also blocks the 20-carboxy-LXB4 formation. These observations suggest that both alcohol dehydrogenase and aldehyde dehydrogenase participate in the oxidation of 20-hydroxy-LXB4 to 20-carboxy-LXB4.

Cloning and sequencing of the cDNA encoding human glutaredoxin

Glutaredoxin (thioltransferase) is a small, heat-stable protein, which is involved in thiol/disulfide exchange reactions. We have isolated a cDNA that encodes glutaredoxin from a human brain cDNA library. The encoded protein contains 106 amino acids with a calculated molecular mass of 11.76 kDa and an isoelectric point of 8.09. The amino acid sequence deduced from the cDNA is more than 80% identical to those of other mammalian glutaredoxins.

Role of Src homology 3 domains in assembly and activation of the phagocyte NADPH oxidase

The phagocyte NADPH oxidase, dormant in resting cells, is activated during phagocytosis to produce superoxide, a precursor of microbicidal oxidants. The activated oxidase is a complex of membrane-integrated cytochrome b558, composed of 91-kDa (gp91phox) and 22-kDa (p22phox) subunits, and two cytosolic factors (p47phox and p67phox), each containing two Src homology 3 (SH3) domains. Here we show that the region of the tandem SH3 domains of p47phox (p47-SH3) expressed as a glutathione S-transferase fusion protein inhibits the superoxide production in a cell-free system, indicating involvement of the domains in the activation. Furthermore, we find that arachidonic acid and sodium dodecyl sulfate, activators of the oxidase in vitro, cause exposure of p47-SH3, which has probably been masked by the C-terminal region of this protein in a resting state. The unmasking of p47-SH3 appears to play a crucial role in the assembly of the oxidase components, because p47-SH3 binds to both p22phox and p67phox but fails to interact with a mutant p22phox carrying a Pro-156-->Gln substitution in a proline-rich region, which has been found in a patient with chronic granulomatous disease. Based on the observations, we propose a signal-transducing mechanism whereby normally inaccessible SH3 domains become exposed upon activation to interact with their target proteins.

Omega-hydroxylation of lipoxin B4 by human neutrophil microsomes: identification of omega-hydroxy metabolite of lipoxin B4 and catalysis by leukotriene B4 omega-hydroxylase (cytochrome P-450LTB omega)

Lipoxin B4 (LXB4) is metabolized either by human neutrophils or by the neutrophil microsomes to a polar compound on a reverse-phase high-performance liquid chromatography. The metabolite is identified as 20-hydroxy-lipoxin B4 (20-OH-LXB4), a novel member in the arachidonic acid cascade, on the basis of ultraviolet spectrometry and gas chromatography-mass spectrometry. The neutrophil microsomes convert LXB4 to its 20-hydroxy derivative under aerobic condition in the presence of NADPH. The reaction is inhibited by carbon monoxide, an inhibitor of cytochrome P-450 (P-450), and by antibodies raised against NADPH-P-450 reductase. A P-450 is thus involved in the omega-hydroxylation of LXB4. The P-450 appears to be the one responsible for leukotriene B4 (LTB4) omega-hydroxylation, P-450LTB omega, based on the following observations. The formation of 20-OH-LXB4 is inhibited solely by substrates of P-450LTB omega such as LTB4 and leukotriene B5 among various fatty acids including prostaglandins. The order of the inhibitory potencies of these substances on the LXB4 omega-hydroxylation is the same as that of their affinities for LTB4 omega-hydroxylase. LTB4 inhibits the reaction in a competitive manner with the Ki value of 0.2 microM, which agrees with the Km value for the LTB4 omega-hydroxylation (0.3 microM).

Formation of a novel 20-hydroxylated metabolite of lipoxin A4 by human neutrophil microsomes

Lipoxin A4 (LXA4) is a biologically active compound produced from arachidonic acid via interactions of lipoxygenases. Incubation of LXA4 either with human neutrophils or with the neutrophil microsomes leads to formation of a polar compound on a reverse-phase high-performance liquid chromatography. We have identified the metabolite as 20-hydroxy-LXA4, a novel metabolite of arachidonic acid, on the basis of ultraviolet spectrometry and gas chromatography-mass spectrometry. The LXA4 omega-hydroxylation requires both molecular oxygen and NADPH, and is inhibited by carbon monoxide, by antibodies raised against NADPH-cytochrome P-450 reductase, or competitively by leukotriene B4 (LTB4) and LTB5, substrates of LTB4 omega-hydroxylase. These findings indicate that the formation of 20-hydroxy-LXA4 is catalyzed by a neutrophil cytochrome P-450, the LTB4 omega-hydroxylase.

Protein synthesis-dependent cytoplasmic translocation of p53 protein after serum stimulation of growth-arrested MCF-7 cells

p53 protein was localized in the cytoplasm of growing and in the nucleus of growth-arrested MCF-7 cells. While the absolute amount and rate of synthesis of p53 in growing and arrested cells were nearly the same, the protein in growing cells was phosphorylated to a greater extent than in arrested cells. The abilities of the cytoplasmic and nuclear p53 proteins to bind to DNA sequences specific for p53 protein binding did not differ remarkably despite their differential phosphorylation levels. Serum-induced translocation of the p53 protein from the nucleus to the cytoplasm, as well as DNA and protein synthesis, were inhibited by cycloheximide. These results suggest that the DNA synthesis-associated cytoplasmic translocation of p53 protein in response to serum stimulation depends on de novo protein synthesis and not on alteration of the protein's ability to bind to specific DNA sequences.

Cytochrome b558, a component of the phagocyte NADPH oxidase, is a flavoprotein

Cytochrome b558 is the only membrane component of the phagocyte O2(-)-producing NADPH oxidase. The O2- production by the oxidase reconstituted in vitro with the crude membrane fraction is enhanced several-fold by addition of FAD, whereas that with the partially purified cytochrome is completely dependent on exogenous FAD, suggesting that FAD acts through the membrane component, cytochrome b558. The alignments of the amino acid sequence of the large subunit of the cytochrome (gp91-phox) with those of previously characterized flavoproteins reveal that the middle and C-terminal portions of gp91-phox are likely to be FAD- and NADPH-binding domains, respectively. Cytochrome b558, thus, appears to be a flavoprotein with an NADPH-binding site, of the NADPH oxidase.

Role of Mg2+ in activation of NADPH oxidase of human neutrophils: evidence that Mg2+ acts through G-protein

The membrane fraction and three cytosolic proteins of neutrophils, p47-phox, p67-phox and a G-protein, are involved in the cell-free activation of the O2(-)-generating NADPH oxidase in the presence of SDS, though it has been controversial whether the G-protein is required or just enhancing the activity. We have used the three cytosolic factors, the solubilized membrane fraction, GTP gamma S and SDS, and found that both G-protein and GTP gamma S are essential for the activation of the NADPH oxidase. The effect of GTP gamma S is modified by Mg2+: the cations enhance the O2- generation at low concentrations of GTP gamma S, whereas they attenuate the activity at higher concentrations of GTP gamma S. In presence of 10 microM GTP gamma S, the maximal activity is observed at 0.1 microM Mg2+, which is several-fold higher than that at 1 mM Mg2+. The omission of Mg2+ followed by the chelation with EDTA results in loss of the activation, which is completely restored by the addition of Mg2+. Thus, Mg2+ seems to modulate the activation of the NADPH oxidase at the level of the G-protein.

HIV-1 Tat acts as a processivity factor in vitro in conjunction with cellular elongation factors

The HIV-1 trans-activator Tat increases the rate of transcription from the HIV-1 LTR promoter through the stem-loop-containing TAR RNA. To analyze the mechanisms of Tat action, a cell-free trans-activation system with no preincubation has been developed. Recombinant Tat specifically increased the level of a long runoff transcript but not a promoter-proximal transcript in a TAR-dependent fashion. These observations and the result of pulse-chase experiments support strongly the hypothesis that Tat enhances the ability of RNA polymerase to elongate over longer distances. Increased levels of the purified cellular factor TFIIF, essential for initiation and also implicated in elongation of transcription, obviated trans-activation by Tat by increasing the basal (Tat-independent) activity. However, another elongation factor, ATN/TFIIS, showed synergistic activation with Tat. An antiserum against a recombinant form of the large subunit of TFIIF (RAP 74) preferentially suppressed the activated level of transcription exerted by Tat. We propose the hypothesis that Tat acts as a processivity factor on RNA polymerase II in an analogous manner to TFIIF.

A quick procedure for purification of functional recombinant proteins over-expressed in E.coli

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Conserved sequence motifs in the small subunit of human general transcription factor TFIIE

A general initiation factor, TFIIE, is essential for transcription initiation by RNA polymerase II in conjunction with other general factors. TFIIE is a heterotetramer containing two subunits of relative molecular mass 57,000 (TFIIE-alpha) and two of 34,000 (TFIIE-beta). TFIIE-beta is required in conjunction with TFIIE-alpha for transcription initiation. Here we report the cloning and expression of a complementary DNA encoding a functional human TFIIE-beta. Recombinant TFIIE-beta could replace the natural TFIIE-beta for transcription in conjunction with TFIIE-alpha. Amino-acid sequence comparisons reveal regions with sequence similarities to: subregion 3 of bacterial sigma factors; a region of RAP30 (the small subunit of TFIIF) with sequence similarity to a sigma-factor subregion implicated in binding to RNA polymerase; and a portion of the basic region-helix-loop-helix motif found in several enhancer-binding proteins. These potential homologies have implications for the role of TFIIE in preinitiation complex assembly and function.

Structural motifs and potential sigma homologies in the large subunit of human general transcription factor TFIIE

The general transcription factor TFIIE has an essential role in eukaryotic transcription initiation together with RNA polymerase II and other general factors. Human TFIIE consists of two subunits of relative molecular mass 57,000 (TFIIE-alpha) and 34,000 (TFIIE-beta) and joins the preinitiation complex after RNA polymerase II and TFIIF. Here we report the cloning and structure of a complementary DNA encoding a functional human TFIIE-alpha. TFIIE-alpha is necessary for transcription initiation together with TFIIE-beta, and recombinant TFIIE-alpha can fully replace the natural subunit in an in vitro transcription assay. The sequence contains several interesting structural motifs (leucine repeat, zinc finger and helix-turn-helix) and sequence similarities to bacterial sigma factors that suggest direct involvement in the regulation of transcription initiation.