title: Myb binding sites within the N-ras promoter repress transcription.
abstract: In vitro and in vivo methods were combined to determine the function of the three Myb binding sites (NrasI, NrasII and NrasIII) within the promoter region of the mouse N-ras gene. We found that the c-Myb DNA-binding domain can bind with high affinity to NrasI and NrasII, but with a reduced affinity to NrasIII. In contrast, the full length v-Myb protein from BM2 cells only bound to the middle one of the three sites, NrasII. Both c-Myb and v-Myb functioned as repressors and reduce the basal activity of the N-ras promoter by 60%, as determined by transient transfection experiments using different regions of the N-ras promoter. This repression required a functional Myb DNA-binding domain and could not be overcome by fusion to the potent VP16 activation domain. In electrophoretic mobility shift assays, the v-Myb protein is shown to be present in different conformations depending on its binding to the NrasII or the mim-1A site. The v-Myb conformation is thus suggested to play a critical role in the regulation of v-Myb activity.
authors.affiliation: Department of Pathology, Stanford University, School of Medicine, California 94305-5324, USA.
authors.forename: B
authors.initials: B
authors.lastname: Ganter
authors.forename: J S
authors.initials: JS
authors.lastname: Lipsick
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002478:Cells, Cultured; D002645:Chickens; D011905:Genes, ras; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011487:Protein Conformation; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D020598:Proto-Oncogene Proteins c-myb; D012097:Repressor Proteins / Q000502:physiology*; D015534:Trans-Activators / Q000502:physiology*; D014162:Transfection
chemical_list: D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D012097:Repressor Proteins; D015534:Trans-Activators