Residues in the WD repeats of Tup1 required for interaction with alpha2.

The yeast transcriptional repressor Tup1 contains seven WD repeats which interact with the DNA-binding protein alpha2. 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 alpha2 resembles the interaction between Gbeta 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.