Transcriptional activation by the myb proteins requires a specific local promoter structure.
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 DNA-binding 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.
Ganter
B
B
Department of Pathology, Stanford University, School of Medicine, Stanford, CA 94305-5324, USA.
Chao
S T
ST
Lipsick
J S
JS
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002478:Cells, Cultured; D004279:DNA, Viral / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D020626:Oncogene Proteins v-myb / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding / Q000235:genetics; D020598:Proto-Oncogene Proteins c-myb / Q000502:physiology*; D011784:Quail; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D015533:Transcriptional Activation / Q000235:genetics*
D004279:DNA, Viral; D004268:DNA-Binding Proteins; D020626:Oncogene Proteins v-myb; D020598:Proto-Oncogene Proteins c-myb