Presence of multiple species of polypeptides immunologically related to transcription factor TFIIIA in adult Xenopus tissues

The 40 kDa 63Ni(2+)-binding protein (pNiXc) on western blots of Xenopus laevis oocytes and embryos is the monomer of fructose-1,6-bisphosphate aldolase A

A Ni(2+)-binding protein (pNiXc, 40 kDa), present in Xenopus laevis oocytes and embryos, was isolated from mature oocytes by chromatography on DEAE-cellulose and cellulose phosphate, followed by FPLC on Ni-iminodiacetate-Agarose, or reverse-phase HPLC on a C-4 column. Size-exclusion HPLC showed that intact pNiXc is approximately 155 kDa, consistent with tetrameric structure. After cleavage with Lys-C proteinase or cyanogen bromide, six peptides were separated by HPLC and sequenced by Edman degradation, providing sequence data for 83 residues. Data-base search showed similarity of pNiXc to eukaryotic aldolases, with 96% identity to human aldolase A. pNiXc demonstrated aldolase activity with fructose 1,6-bisphosphate as substrate (Km, 30 microM Vmax 26 mumol min-1 mg-1); the aldolase activity was inhibited non-competitively by Cu2+, Cd2+, Co2+, or Ni2+. Equilibrium dialysis showed high affinity binding (Kd, 7 microM) of 1 mole of Ni per mole of 40 kDa subunit. Based on metal-blot competition assays, the abilities of metals to compete with 63Ni2+ for binding to pNiXc were ranked: Cu2+ >> Zn2+ > Cd2+ > Co2+. This study identifies pNiXc as the monomer of fructose-1,6-bisphosphate aldolase A, and raises the possibility that aldolase A is a target enzyme for metal toxicity.

Definition of the binding sites of individual zinc fingers in the transcription factor IIIA-5S RNA gene complex

A series of polypeptides containing increasing numbers of zinc fingers of Xenopus transcription factor IIIA has been generated and binding to the 5S RNA gene internal control region has been studied in order to elucidate the mode of interaction of the individual fingers with DNA. By using a combination of DNase I footprinting, methylation interference, and differential binding to mixtures of DNA fragments differing in length by single base pairs, the binding sites for individual fingers have been defined. These results have led to a model for the interaction of transcription factor IIIA with the internal control region in which fingers 1-3 bind in the major groove of the promoter C block, fingers 7-9 bind in the major groove of the A block, and finger 5 binds in the major groove of the intermediate element. Fingers 4 and 6 each bind across the minor groove, spanning these promoter elements.

Expression of transforming growth factor alpha in human tissues: immunohistochemical study and northern blot analysis

The expression of transforming growth factor alpha (TGF-alpha) was examined in various human tissues and the fetus, using immunohistochemistry and Northern blot analysis. TGF-alpha immunoreactivity was detected mainly in the epithelial cells of the digestive tract, liver, pancreas, kidney, thyroid, adrenal, skin, mammary gland and genital organs. In the digestive tract, epithelial cells with regenerative change or hyperplastic change showed strong immunoreactivity to TGF-alpha. Peripheral nerve, vessels, megakaryocytes and macrophages in the lung and spleen were also positive for TGF-alpha. By Northern blot analysis the expression of TGF-alpha mRNA was confirmed in the digestive tract, salivary gland, thyroid, kidney and mammary gland. In the human fetus, the nerve tissues, liver, adrenal and kidney were positive for TGF-alpha. Strong immunoreactivity to TGF-alpha was observed in the hepatocytes of the fetus. These findings indicate that TGF-alpha is produced by a variety of non-neoplastic cells in both adult and fetal tissues.

Detection of two Zn-finger proteins of Xenopus laevis, TFIIIA, and p43, by probing western blots of ovary cytosol with 65Zn2+, 63Ni2+, or 109Cd2+

Two Zn-finger proteins, TFIIIA (a constituent of 7S RNP particles) and p43 (a constituent of 42S RNP particles), were detected in ovary extracts of juvenile Xenopus laevis females by in vitro binding of radiolabeled divalent metals. Proteins fractionated by SDS-PAGE (sodium dodecylsulfate-polyacrylamide gel electrophoresis) were transferred by Western blotting onto nitrocellulose membranes, probed with 65Zn2+, 63Ni2+, or 109Cd2+, and visualized by autoradiography. Detection limits for TFIIIA were approx 0.07 micrograms/well by 109Cd(2+)-probing, 0.13 micrograms/well by 65Zn(2+)-probing, and 0.26 mu/well by 63Ni(2+)-probing. Protein p43 was more clearly visualized by probing with 63Ni2+ than with 65Zn2+ or 109Cd2+. After purified TFIIIA was cleaved with cyanogen bromide, 65Zn2+, 109Cd2+, and 63Ni2+ distinctly labeled the 22 kDa middle fragment; 65Zn2+ and 109Cd2+ also labeled the 11 kDa N-terminal fragment, but did not label the 13 kDa C-terminal fragment. These results are consistent with the notion that the radioligands were bound to finger-loop domains of TFIIIA, which occur in the middle and N-terminal fragments. Based on the abilities of nonradioactive metal ions to compete with 65Zn2+ for binding to TFIIIA on Western blots, the relative affinities of the metals for TFIIIA were ranked as follows: Zn2+ = Cu2+ greater than or equal to Hg2+ greater than Cd2+ greater than Co2+ greater than or equal to Ni2+. Even at a 1000-fold molar excess, Mn2+ did not compete with 65Zn2+ for binding to TFIIIA. Probing Western blots with the radiolabeled metal ions greatly facilitates the detection, isolation, and quantitation of TFIIIA and p43.

Yeast TFIIIA + TFIIIC/tau-factor, but not yeast TFIIIA alone, interacts with the Xenopus 5S rRNA gene

The successful use of mixed heterologous in vitro transcription systems has suggested that the species specificity of RNA polymerase III transcription is low. To see if this extends to lower eukaryotic class III transcription factors, we compared the interactions of the two yeast assembly factors, TFIIIA and TFIIIC/tau factor, with a homologous yeast 5S rRNA gene and a heterologous Xenopus laevis somatic 5S rRNA gene. Transcription assays showed that the Xenopus gene was transcriptionally inactive in a crude cell-free yeast extract that actively transcribes the homologous gene. However, the Xenopus gene was still able to compete for limiting transcription factors. Electrophoretic DNA binding assays revealed that while TFIIIA bound avidly to the yeast gene (generating the 'A-complex'), it had no affinity for the Xenopus 5S rRNA gene. Nevertheless, a complex of both TFIIIA and TFIIIC/tau factor (the 'AC-complex') was formed on the two genes with similar affinity, although only the complex assembled on the homologous gene was able to activate transcription. Thus enough sequence information is present on the heterologous gene to direct transcription factor assembly, but not to activate transcription. Like its counterpart in Xenopus, the yeast TFIIIA appears to be a zinc binding protein that is inactivated by EDTA and 1,10-phenanthroline, and reactivated in the presence of zinc ions. Bound to the 5S rRNA gene, TFIIIA is however significantly more resistant to inactivation by chelators than in its free state. The AC-complex differs from the A-complex by being less affected by chelators, and by being more sensitive to the dissociating effect of single-stranded DNA.

Xenopus transcription factor IIIA (XTFIIIA): after a decade of research

Xenopus transcription factor IIIA (XTFIIIA) is the first eukaryotic transcription factor purified to homogeneity and is specifically required for the 5S RNA gene transcription. It contains two structural domains and nine zinc finger motifs through which it recognizes the promoter region of the 5S RNA gene. It also binds to 5S RNA and serves to store 5S RNA in the form of 7S ribonucleoprotein particles in oocytes. Additionally, it forms a metastable complex with 5S DNA and promotes the formation of stable and competent transcription complexes. Its expression is developmentally controlled at the level of transcription and translation. Moreover, it participates in the assembly of active chromatin templates and at least, in part, is responsible for the developmental regulation of two kinds of 5S RNA genes in Xenopus.

Physical and immunological characterization of human transcription factor IIIA

Human transcription factor IIIA (htFIIIA), specifically required for transcription of the gene for 5S ribosomal RNA has been characterized with respect to some of its physical, immunological and functional properties. TFIIIA from HeLa cells, which selectively binds 5S RNA, is a monomer of approximately 35 kDa with a Stokes' radius of approximately 2.65 nm and a sedimentation coefficient of approximately 2.8 S. These values indicate that the human protein is of rather globular shape and hence diverges not only in molecular mass but also in most of the molecular properties from its highly asymmetric counterpart in Xenopus laevis oocytes. By raising specific polyclonal antibodies against hTFIIIA it was shown in Western immunoblots that there was no cross-reaction between anti-hTFIIIA antibodies and the amphibian protein. Conversely, monoclonal antibodies against three domains of X. laevis TFIIIA antibodies and the amphibian protein. Conversely, monoclonal antibodies against three domains of X. laevis TFIIIA did not cross-react with the human transcription factor. The polyclonal antisera raised against hTFIIIA specifically neutralized binding of the human transcription factor to 5S DNA and abolished in vitro transcription of 5S RNA but these antibodies were unable to inhibit 5S RNA synthesis in cellular extracts from Xenopus, Drosophila or yeast cells. Finally, the species variation of TFIIIA could be substantiated by electrophoretic mobility shift assays revealing preferential binding of hTFIIIA to the homologous 5S RNA gene.