Transcriptional activation by the Myb proteins requires a specific local promoter structure

Abstract

The biological effects of the cellular c-Myb and the viral v-Myb proteins are strikingly different. While c-Myb is indispensable for normal hematopoiesis, v-Myb induces acute leukemia. The v-Myb DNA-binding domain (DBD) differs from that of c-Myb mainly by deletion of the first of three repeats which correlates with efficient oncogenic transformation and a decrease in DNA-binding activity. To investigate the difference in DNA-binding and transcriptional activation, oligonucleotide selection and electrophoretic mobility shift assays were employed. The v-Myb DBD (R2R3) shows an intrinsic DNAbinding specificity for an AT-rich downstream extension of the Myb recognition element (MRE) PyAAC T / G G for efficient binding to this site, whereas R1 within the c-Myb DBD allows for more flexibility for this downstream extension. Therefore, due to the presence of repeat R1, c-Myb can bind to a greater number of target sites. The intrinsic DNA-binding specificity of R2R3 is further supported with the results from in vivo transcriptional activation experiments which demonstrated that both the v-Myb and c-Myb DBDs require an extension of the MRE (motif #1) by a downstream T-stretch (motif #2) for full activity. Surprisingly, the T-stretch improves binding when present on either strand, but is required on a specific strand for transcriptional activation.z 1999 Federation of European Biochemical Societies.

Novel Core Promoter Elements and a Cognate Transcription Factor in the Divergent Unicellular Eukaryote Trichomonas vaginalis

“…It should be noted, however, that our data do not preclude the possibility that a subset of promoters may use one or more of the previously (36,42,56) and/or M3BP, discussed below. The M3 consensus sequence, (A/G/T)(A/G)C(G/C)G(T/C) T(T/A/G), strongly resembles the classic eukaryotic MRE, Py-AAC(T/G)G, which is found in distal promoter regions of genes in a broad range of eukaryotes and acts to regulate an array of developmental processes (19,30,49). For example, in humans, the MRE is recognized by a family of Myb proteins (c-Myb, A-Myb, and B-Myb) that regulate processes such as hematopoiesis and spermatogenesis (38,49).…”

Multifarious Transcriptional Regulation of Adhesion Protein Gene ap65 - 1 by a Novel Myb1 Protein in the Protozoan Parasite Trichomonas vaginalis

“…As suggested by the DNA binding specificity assay, rMyb1 may simply recognize a 5Ј core sequence, ATCG, for initial weak binding, and the binding affinity might be greatly enhanced in the presence of a 3Ј accessory sequence, TNTT, on the DNA element. Such a DNA binding specificity is reminiscent of that of the vertebrate c-Myb protein, which recognizes a promoter context with a 5Ј core sequence, c/tAACt/gG, for partial binding and a downstream stretch of T's for full activity (10). Intriguingly, either MRE-1/MRE-2r or MRE-2f was sufficient for repression of basal activity (Fig.…”

The transcription factor B-Myb is essential for S-phase progression and genomic stability in diploid and polyploid megakaryocytes

“…Of the vertebrate Myb proteins, B-Myb appears to be the one most related to the single Drosophila Myb protein (Dm-Myb) (Ganter et al, 1999;Simon et al, 2002). Dm-Myb has been shown to be essential for development (Katzen and Bishop, 1996;Fitzpatrick et al, 2002;Manak et al, 2002).…”