Residues in the WD repeats of Tup1 required for interaction with alpha 2

The yeast transcriptional repressor Tup1 contains seven WD repeats which interact with the DNA-binding protein alpha 2. We have identified mutations in Tup1 that disrupt this interaction. The positions of the amino acids changed by these mutations are consistent with Tup1 being folded into a seven-bladed propeller like that formed by another WD repeat-containing protein, the beta subunit of the heterotrimeric G protein used in signal transduction. Our results also indicate that the interaction between Tup1 and alpha 2 resembles the interaction between G beta and G alpha, suggesting that a similar structural interface is formed by WD repeat proteins that are used in both transcriptional regulation and signal transduction.