Functional domains of the human B-myb gene product.

Three members of the human myb gene family (c-myb, A-myb, and B-myb) encode transcriptional regulators that can bind to specific DNA sequences. High levels of c-myb expression are usually found in immature hemopoietic cells, but the B-myb is more commonly expressed in many types of cells. To understand the regulation of the activity of B-myb gene product (B-Myb), its functional domains were analyzed. Like c-Myb, B-Myb also has a transcriptional activation domain containing a cluster of acidic amino acids in the region downstream of the DNA-binding domain, which consists of three tandem repeats of 51-52 amino acids. In contrast to c-Myb, B-Myb does not contain a negative regulatory domain. Furthermore, the multiple nuclear localization signals are in at least two regions in the COOH-terminal half of B-Myb, and one of them is adjacent to a potential cdc2 kinase site. These results indicate that B-Myb contains DNA-binding and transcriptional activation domains similar to those of c-Myb, but a regulatory mechanism of B-Myb activity is quite different from that for c-Myb.