INTERACTION OF BTG1 AND P53-REGULATED BTG2 GENE-PRODUCTS WITH MCAF1, THE MURINE HOMOLOG OF A COMPONENT OF THE YEAST CCR4 TRANSCRIPTIONAL REGULATORY COMPLEX

Both BTG1 and BTG2 are involved in cell-growth control. BTG2 expressio n is regulated by p53, and its inactivation in embryonic stem cells le ads to the disruption of DNA damage-induced G(2)/M cell-cycle arrest. In order to investigate the mechanism underlying Btg-mediated function s, we looked for possible functional partners of Btg1 and Btg2. Using yeast two-hybrid screening, protein-binding assays, and transient tran sfection assays in HeLa cells, we demonstrated the physical in vitro a nd in vivo interaction of both Btg1 and Btg2 with the mouse protein mC af1 (i.e. mouse CCR4-associated factor 1). mCaf1 was identified throug h its interaction with the CCR4 protein, a component of a general tran scription multisubunit complex, which, in yeast, regulates the express ion of different genes involved in cell-cycle regulation and progressi on, These data suggest that Btg proteins, through their association wi th mCaf1, may participate, either directly or indirectly, in the trans criptional regulation of the genes involved in the control of the cell cycle. Finally, we found that box B, one of two conserved domains whi ch define the Btg family, plays a functional role, namely that it is e ssential to the Btg-mCaf1 interaction.