The viral erbA oncogene protein, a constitutive repressor in animal cells, is a hormone-regulated activator in yeast.

The v-erbA oncogene is a retrovirus-transduced and altered copy of a cellular gene for a thyroid hormone receptor. In animal cells, the v-erbA protein fails to respond to hormone and acts as a dominant negative allele, inhibiting gene activation normally conferred by the wild-type thyroid hormone receptor. We report here that, unexpectedly, the v-erbA protein acts as a hormone-regulated transcriptional activator in S. cerevisiae. We suggest that the ability of v-erbA protein to function as a transcriptional repressor or an activator is determined by interaction with, or modification by, other cellular factors, and that this phenomenon may be relevant to understanding ligand regulation of the normal thyroid and steroid hormone receptors.