The Neurospora crassa blind mutant white collar‐1 (wc‐1) is pleiotropically defective in all blue light‐induced phenomena, establishing a role for the wc‐1 gene product in the signal transduction pathway. We report the cloning of the wc‐1 gene isolated by chromosome walking and mutant complementation. The elucidation of the wc‐1 gene product provides a key piece of the blue light signal transduction puzzle. The wc‐1 gene encodes a 125 kDa protein whose encoded motifs include a single class four, zinc finger DNA binding domain and a glutamine‐rich putative transcription activation domain. We demonstrate that the wc‐1 zinc finger domain, expressed in Escherichia coli, is able to bind specifically to the promoter of a blue light‐regulated gene of Neurospora using an in vitro gel retardation assay. Furthermore, we show that wc‐1 gene expression is autoregulated and is transcriptionally induced by blue light irradiation.

Oxidative conditions must be generated in the endoplasmic reticulum (ER) to allow disulfide bond formation in secretory proteins. A family of conserved genes, termed ERO for ER oxidoreductins, plays a key role in this process. We have previously described the human gene ERO1-L, which complements several phenotypic traits of the yeast thermo-sensitive mutant ero1-1

Oxidizing conditions must be maintained in the endoplasmic reticulum (ER) to allow the formation of disulfide bonds in secretory proteins. Here we report the cloning and characterization of a mammalian gene (ERO1-L) that shares extensive homology with the Saccharomyces cerevisiae ERO1 gene, required in yeast for oxidative protein folding. When expressed in mammalian cells, the product of the human ERO1-L gene colocalizes with ER markers and displays Endo-H-sensitive glycans. In isolated microsomes, ERO1-L behaves as a type II integral membrane protein. ERO1-L is able to complement several phenotypic traits of the yeast thermosensitive mutant ero1-1, including temperature and dithiothreitol sensitivity, and intrachain disulfide bond formation in carboxypeptidase Y. ERO1-L is no longer functional when either one of the highly conserved Cys-394 or Cys-397 is mutated. These results strongly suggest that ERO1-L is involved in oxidative ER protein folding in mammalian cells.

The presence of correctly formed disul®de bonds is crucial to the structure and function of proteins that are synthesized in the endoplasmic reticulum (ER). Disul®de bond formation occurs in the ER owing to the presence of several specialized catalysts and a suitable redox potential. Work in yeast has indicated that the ER resident glycoprotein Ero1p provides oxidizing equivalents to newly synthesized proteins via protein disul®de isomerase (PDI). Here we show that Ero1-La, the human homolog of Ero1p, exists as a collection of oxidized and reduced forms and covalently binds PDI. We analyzed Ero1-La cysteine mutants in the presumed active site C 391 VGCFKC 397 . Our results demonstrate that this motif is important for protein folding, structural integrity, protein half-life and the stability of the Ero1-La±PDI complex.

Interleukin‐6 (IL‐6) is a differentiation and growth factor for a variety of cell types and its excessive production plays a major role in the pathogenesis of multiple myeloma and post‐menopausal osteoporosis. IL‐6, a four‐helix bundle cytokine, is believed to interact sequentially with two transmembrane receptors, the low‐affinity IL‐6 receptor (IL‐6R alpha) and the signal transducer gp130, via distinct binding sites. In this paper we show that combined mutations in the predicted A and C helices, previously suggested to establish contacts with gp130, give rise to variants with no bioactivity but unimpaired binding to IL‐6R alpha. These mutants behave as full and selective IL‐6 receptor antagonists on a variety of human cell lines. Furthermore, a bifacial mutant was generated (called IL‐6 super‐antagonist) in which the antagonist mutations were combined with amino acid substitutions in the predicted D helix that increase binding for IL‐6R alpha. The IL‐6 super‐antagonist has no bioactivity, but improved first receptor occupancy and, therefore, fully inhibits the wild‐type cytokine at low dosage. The demonstration of functionally independent receptor binding sites on IL‐6 suggests that it could be possible to design super‐antagonists of other helical cytokines which drive the assembly of structurally related multisubunit receptor complexes.