In Saccharomyces cerevisiae, expression of arginine catabolic genes CAR1 and CAR2 in response to exogenous nitrogen availability is mediated by the Ume6 (CargRI)-Sin3 (CargRII)-Rpd3 (CargRIII) complex

The products of three genes named CARGRI, CARGRII, and CARGRIII were shown to repress the expression of CAR1 and CAR2 genes, involved in arginine cata bolism, CARGRI is identical to UME6 and encodes a regulator of early meioti c genes. In this work we identify CARGRII as SIN3 and CARGRIII as RPD3. The associated gene products are components of a high-molecular-weight complex with histone deacetylase activity and are recruited by Ume6 to promoters c ontaining a URS1 sequence. Sap30, another component of this complex, is als o required to repress CARI expression. This histone deacetylase complex pre vents the synthesis of the two arginine catabolic enzymes, arginase (CARI) and ornithine transaminase (CAR2), as long as exogenous nitrogen is availab le. Upon nitrogen depletion, repression at URS1 is released and Ume6 intera cts with ArgRI and ArgRII, two proteins involved in arginine-dependent acti vation of CARI and CAR2, leading to high levels of the two catabolic enzyme s despite a low cytosolic arginine pool. Our data also show that the deleti on of the UME6 gene impairs cell growth more strongly than the deletion of the SIN3 or RPD3 gene, especially in the Sigma 1278b background.