We have isolated a complementary DNA clone containing sequences homologous to those encoding the alpha-subunit of a mouse muscle nicotinic acetylcholine receptor. Based on the structural similarities between the encoded protein and the muscle acetylcholine receptor alpha-subunit, and the presence of hybridizing RNA species in the brain, we propose that this clone codes for a neural nicotinic acetylcholine receptor alpha-subunit.

The gene encoding the auxin-responsive GH3 mRNA (G. Hagen, A. Kleinschmidt, TJ. Guilfoyle, Planta 162: 147-153 (1984] from soybean was cloned, and its sequence and transcription initiation site were determined. The promoter of the GH3 gene has been fused to the open reading frame of the Escherichia coli uidA gene which encodes beta-glucuronidase (GUS). This fusion gene was introduced into tobacco via Agrobacterium tumefaciens-mediated transformation, and the expression of the gene was examined by fluorometric assay and histochemical staining of young R1 tobacco seedlings and mature plants. In transgenic tobacco plants that have not been exposed to exogenous auxin, expression of the fusion gene is largely restricted to roots of young green plants and developing floral organs, including ovules, developing seeds, and pollen, of mature plants. Application of exogenous auxin to tobacco seedlings or plant organs results in a greater than 50-fold increase in expression of GUS. Auxin-induced GUS expression is greatest in vascular tissue, but not restricted to this tissue. The auxin-deduced GUS expression was characterized for kinetics, auxin specificity and dose response.

A 4-kilobase and a 2-kilobase cDNA clone encoding a murine macrophage colony-stimulating factor have been isolated. Except for 2 amino acid residue differences, these two clones encode the same 520 amino acid residue protein, which is preceded by a 32-amino acid residue signal peptide. The two clones, whose molecular masses correspond to the two transcripts observed in murine L929 fibroblasts, contain 3' untlated regions that are markedly different in sequence and length. Both clones can be expressed in COS cells and the recombinant protein is active in a mouse bone marrow colony assay.

The mouse cell line BC3H-I synthesizes an acetylcholine receptor (AChR) with the pharmacological properties of a muscle nicotinic cholinergic receptor. We have purified mRNA from this cell line and used the size-fractionated poly(A)+RNA to produce a cDNA library of approximately 50,000 clones. The library was screened with a subclone containing genomic sequences coding for the putative acetylcholine-binding site of the alpha-subunit of chicken AChR. We obtained a plasmid, pMAR alpha 15, with a 1,717-base pair insert. The insert cDNA has 26 nucleotides at the 5'-end which code for a portion of the signal peptide followed by a single open reading frame of 1,311 nucleotides which code for a protein of 49,896 daltons. The insert has 377 bases of 3'-untranslated sequence with 3 polyadenylation sites. Radiolabeled plasmid DNA has been used to identify homologous RNA species of about 2 kilobases in Northern blot analyses of poly(A)+ selected RNA from BC3H-I cells. A similar size mRNA is seen in innervated mouse diaphragm and leg muscle, and both mouse and rat brain. Comparisons of the deduced amino acid sequence of the mouse AChR alpha-subunit with Torpedo marmorata, T. californica, chicken, human, and calf sequences show overall homologies of 80%, 80%, 86%, 96%, and 95%, respectively. More detailed analyses reveal a non-random distribution of amino acid substitutions in several structural domains. Based on the absolute conservation of cysteine residues, a new model for the arrangement of the disulfide bonds in the extracellular portion of the alpha-subunit is proposed.

Twenty-three monoclonal antibodies (MAbs) against the IL-2 receptor alpha-chain (CD25) were evaluated as ricin A-chain immunotoxins for the treatment of Hodgkin's disease. Primary screening used an indirect assay in which the cells were treated with the test antibody followed by a Fab' immunotoxin against mouse immunoglobulin. This screening identified 5 MAbs which inhibited protein synthesis in L540 Hodgkin cells by 50% at a concentration (IC50) of 6 x 10(-11) M or less: RFT5 gamma 1, RFT5 gamma 2a, B-B10, B-F2 and B-G3. These MAbs were then linked directly to deglycosylated ricin A-chain (dgA) and were confirmed to have potent and specific toxicity for L540 cells. The immunotoxins had the following potency order: RFT5 gamma 1 greater than RFT5 gamma 2a greater than B-B10 greater than B-F2 greater than B-G3. The most effective immunotoxin, RFT5 gamma 1.dgA, had an IC50 value of 7 x 10(-12) M, which is the same as that of whole ricin. In vivo, a single intravenous injection of 48 micrograms of RFT5 gamma 1.dgA, RFT5 gamma 2a.dgA, B-B10.dgA or B-F2 induced lasting complete remissions in 78, 66, 50 and 44%, respectively, of nude mice bearing subcutaneous solid L540 tumours of 0.7 cm diameter. Two tumours which regrew after B-B10.dgA treatment were re-established in tissue culture. Both had reduced sensitivity to B-B10.dgA in vitro but not to immunotoxins recognizing different antigens on Hodgkin cells. The MAbs that produced the most potent immunotoxins, RFT5 gamma 1, RFT5 gamma 2a and B-B10, had no significant cross-reactivity with normal human tissues outside the lymphoid system as judged from indirect immunoperoxidase staining of frozen sections. By contrast, B-F2 strongly stained normal human renal tubules.