trans activation of gene expression by v-myb.

The v-myb oncogene causes acute myelomonocytic leukemia in chickens and transforms avian myeloid cells in vitro. Its product, p48v-myb, is a short-lived nuclear protein which binds DNA. We demonstrate that p48v-myb can function as a trans activator of gene expression in transient DNA transfection assays. trans activation requires the highly conserved amino-terminal DNA-binding domain and the less highly conserved carboxyl-terminal domain of p48v-myb, both of which are required for transformation. Multiple copies of a consensus sequence for DNA binding by p48v-myb inserted upstream of a herpes simplex virus thymidine kinase promoter are strongly stimulatory for transcriptional activation by a v-myb-VP16 fusion protein but not by p48v-myb itself, suggesting that the binding of p48v-myb to DNA may not be sufficient for trans activation.