Springael, J. Y: Both ubiquitin ligase Npi1/Rsp5 and ubiquitin hydrolase Npi2/Doa4 are required for ammonium-induced inactivation and degradation of the general amino-acid permease (Gap1) of Saccharomyces cerevisiae : 14th SMYTE (Small Meeting on Yeast Transport and Energetics) held in Bonn (Germany), September 6-9, 1996