In Saccharomyces cerevisiae, which uses the nonlinear pathway of arginine biosynthesis, the first two enzymes, N-acetylglutamate synthase (NAGS) andN-acetylglutamate kinase (NAGK), are controlled by feedback inhibition. We have previously shown that NAGS andNAGKassociate in a complex, essential to synthase activity and protein level [Abadjieva,A., Pauwels,K.,Hilven, P.&Crabeel,M. (2001) , 42869–42880].