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 catabolism. CARGRI is identical to UME6 and encodes a regulator of early meiotic 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 containing a URS1 sequence. Sap30, another component of this complex, is also required to repress CAR1 expression. This histone deacetylase complex prevents the synthesis of the two arginine catabolic enzymes, arginase (CAR1) and ornithine transaminase (CAR2), as long as exogenous nitrogen is available. Upon nitrogen depletion, repression at URS1 is released and Ume6 interacts with ArgRI and ArgRII, two proteins involved in arginine-dependent activation of CAR1 and CAR2, leading to high levels of the two catabolic enzymes despite a low cytosolic arginine pool. Our data also show that the deletion of the UME6 gene impairs cell growth more strongly than the deletion of the SIN3 or RPD3 gene, especially in the Sigma1278b background.