Repression and activation domains of Rme1p structurally overlap, but differ in requirements

Rme1p, a repressor of meiosis in the yeast Saccharomyces cerevisiae, acts as both a transcriptional repressor and activator. Rmelp is a zinc-finger protein with no other homology to any protein of known function. The C-terminal DNA binding domain of Rmelp is essential for function. We find that mutations and progressive deletions in all three zinc fingers can be rescued by fusion of RME1 to the DNA binding domain of another protein. Thus, structural integrity of the zinc fingers is not required for the Rme1p-mediated effects on transcription. Using a series of mutant Rme1 proteins, we have characterized domains responsible for repression and activation. We find that the minimal transcriptional repression and activation domains completely overlap and lie in an 88-amino-acid N-terminal segment (aa 61-148). An additional transcriptional effector determinant lies in the first 31 amino acids of the protein. Notwithstanding the complete overlap between repression and activation domains of Rmelp, we demonstrated a functional difference between repression and activation: Rgr1p and Sin4p are absolutely required for repression but dispensable for activation.