Members of the basic helix-loop-helix (bHLH) family are required for a number of different developmental pathways, including lymphopoiesis, myogenesis, neurogenesis, and sex determination. Screening a cDNA library prepared from silk-producing glands of the black widow spider, we have identified a new bHLH transcription factor named SGSF. Within the bHLH region, SGSF showed considerable conservation with other HLH proteins, including Drosophila melanogaster achaete and scute, as well as three HLH proteins identified by gene prediction programs. The expression pattern of SGSF was restricted to a subset of silk-producing glands, which include the tubuliform and major ampullate glands. SGSF was capable of binding an E-box element as a heterodimer with the E protein, E47, but was unable to bind this motif as a homodimer. SGSF was demonstrated to be a nuclear transcription factor capable of attenuating the transactivation of E47 homodimers in mammalian cells. SGSF represents the first example of a silk gland-restricted bHLH protein, and its expression pattern suggests that SGSF plays a role in regulating differentiation of cells in the spider that control silk gland formation or egg case silk gene expression.
himself equal to their tasks, a true comrade, who accepted their code of courage and honor. The fact that he wore spectacles was against him at the outset, because they associated spectacles with Eastern schoolmasters and incompetence. They called him "Four Eyes," at first with derision, but they soon discovered that in him they had no "tenderfoot" to deal with. He shot as well as the best of them; he rode as far; he never complained of food or tasks or hardship; he met every one on equal terms. Above all, he left no doubt as to his courage. He would not pick a quarrel nor would he avoid one.
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