J Mol Med (Berl) 1997 Jan 01;7511-12:815-9. doi: 10.1007/s001090050170.

B-Myb, a repressed trans-activating protein.

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B-Myb belongs to a family of related transcription factors which share a unique DNA binding domain. B-Myb plays an important role in regulation of the cell cycle. Its expression is upregulated by the human papilloma virus HPV16 E7 oncoprotein. Overexpression of B-Myb can bypass p53-mediated cell cycle arrest. The founding member of the myb gene family, c-Myb, and A-Myb are involved in hematopoiesis and neurogenesis, respectively, and are both activators of gene transcription. Whether B-Myb is a transactivator or a repressor, however, has remained a matter of discussion. We reviewed the transactivation potential of B-Myb in yeast, taking advantage of the fact that inducible gene activation is an evolutionarily conserved process. By mutational analysis we localized a conserved activation domain in B-Myb. In vertebrate cells the transactivation potential of B-Myb is concealed by the C-terminal part of the protein. We show that the cell cycle regulators cyclin A and cyclin E activate B-Myb by eradicating the inhibition mediated by its carboxy-terminus. Our data suggest that in vertebrates the trans-activating function of B-Myb is regulated during the cell cycle and link Myb functions to cell cycle progression.

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Species referenced: Xenopus
Genes referenced: myb mybl2 tp53