The chicken A-myb protein is a transcriptional activator

c-myb encodes a trans-activator that is essential for the proliferation of most hematopoietic precursor cells but lacks a major role in non-hematopoietic cells. The recent identification of two myb-related genes (A-myb and B-myb) in several vertebrate species has raised the possibility that these genes perform c-myb like functions in non-hematopoietic cells. Here, we report the isolation and preliminary characterization of the chicken A-myb gene. Like other members of the myb family, the A-myb protein contains an N-terminally located repeat domain that is highly homologous to the DNA-binding domain of the c-myb protein. Unlike c-myb, A-myb is expressed in fibroblasts, suggesting that it functions in non-hematopoietic cells. We demonstrate that A-myb transactivates myb-responsive reporter genes. Furthermore, when stably expressed in a chicken macrophage cell line. A-myb causes activation of several myb-inducible endogenous genes. These findings show that A-myb encodes a transactivating member of the myb family whose functional properties resemble those of the c-myb and v-myb proteins. Thus, our results support the idea that A-myb is a functional equivalent of c-myb.