THE CHICKEN A-MYB PROTEIN IS A TRANSCRIPTIONAL ACTIVATOR

c-myb encodes a trans-activator that is essential for the proliferatio n of most hematopoietic precursor cells but lacks a major role in non- hematopoietic cells. The recent identification of two myb-related gene s (A-myb and B-myb) in several vertebrate species has raised the possi bility that these genes perform c-myb like functions in non-hematopoie tic cells. Here, we report the isolation and preliminary characterizat ion of the chicken A-myb gene. Like other members of the myb family, t he A-myb protein contains an N-terminally located repeat domain that i s highly homologous to the DNA-binding domain of the c-myb protein. Un like c-myb, A-myb is expressed in fibroblasts, suggesting that it func tions in non-hematopoietic cells. We demonstrate that A-myb transactiv ates 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 encode s a transactivating member of the myb family whose functional properti es resemble those of the c-myb and v-myb proteins. Thus, our results s upport the idea that A-myb is a functional equivalent of c-myb.