| Mammalian Sug 1 and c Fos in the nuclear 26S proteasome . ^^^ In a search for regulatory proteins that interact with the leucine zipper motif of c Fos in the yeast two hybrid screen , we have identified a protein ( FZA B ) that has extensive sequence similarity to SUG 1 of Saccharomyces cerevisiae . ^^^ Here we show that FZA B can functionally substitute for SUG 1 in yeast and that FZA B interacts with Fos proteins in vitro through their leucine zippers . ^^^ |