Two regions in c-myb proto-oncogene product negatively regulating its DNA-binding activity

The c-myb proto-oncogene product (c-Myb) is a transcriptional regulator that binds to the specific DNA sequence. Deletion of the negative regulatory domain (NRD) in the carboxyl-proximal region of c-Myb results in both increased trans-activating capacity and oncogenic activation. One possible mechanism to modulate c-Myb activity is a regulation of DNA-binding activity. However, it is not known whether any region in NRD affects the in vivo DNA-binding activity of c-Myb. Using the highly transfectable cell line 293T, we developed a system to precisely measure the DNA-binding activity of Myb expressed in mammalian cells. Using this system, two regions in NRD were shown to repress DNA-binding activity. These results suggest that DNA-binding activity of c-Myb is independently regulated by multiple mechanisms through these subdomains.