Differential interactions between Brother proteins and Runt domain proteins in the Drosophila embryo and eye.
Brother and Big brother were isolated as Runt-interacting proteins and are homologous to CBF(beta), which interacts with the mammalian CBF(alpha) Runt-domain proteins. In vitro experiments indicate that Brother family proteins regulate the DNA binding activity of Runt-domain proteins without contacting DNA. In both mouse and human there is genetic evidence that the CBF(alpha) and CBF(beta) proteins function together in hematopoiesis and leukemogenesis. Here we demonstrate functional interactions between Brother proteins and Runt domain proteins in Drosophila. First, we show that a specific point mutation in Runt that disrupts interaction with Brother proteins but does not affect DNA binding activity is dysfunctional in several in vivo assays. Interestingly, this mutant protein acts dominantly to interfere with the Runt-dependent activation of Sxl-lethal transcription. To investigate further the requirements for Brother proteins in Drosophila development, we examine the effects of expression of a Brother fusion protein homologous to the dominant negative CBF(beta)::SMMHC fusion protein that is associated with leukemia in humans. This Bro::SMMHC fusion protein interferes with the activity of Runt and a second Runt domain protein, Lozenge. Moreover, we find that the effects of lozenge mutations on eye development are suppressed by expression of wild-type Brother proteins, suggesting that Brother/Big brother dosage is limiting in this developmental context. Results obtained when Runt is expressed in developing eye discs further support this hypothesis. Our results firmly establish the importance of the Brother and Big brother proteins for the biological activities of Runt and Lozenge, and further suggest that Brother protein function is not restricted to enhancing DNA-binding.
Department of Biochemistry and Cell Biology and the Institute for Cell and Developmental Biology, SUNY at Stony Brook, Stony Brook, NY 11794-5215, USA.
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D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D004330:Drosophila / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology; D029721:Drosophila Proteins; D005123:Eye / Q000254:growth & development*; D018507:Gene Expression Regulation, Developmental; D017344:Genes, Insect; D006801:Humans; D019476:Insect Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D009687:Nuclear Proteins; D017354:Point Mutation; D016601:RNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology
D017931:DNA Primers; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D019476:Insect Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; C067777:Sxl protein, Drosophila; D014157:Transcription Factors; C099964:lz protein, Drosophila; C080833:run protein, Drosophila