ArgRII, a component of the ArgR-Mcm1 complex involved in the control of arginine metabolism in Saccharomyces cerevisiae, is the sensor of arginine

Repression of arginine anabolic genes and induction of arginine catabolic g enes are mediated by a three-component protein complex, interacting with sp ecific DNA sequences in the presence of arginine, Although ArgRI and Mcm1, two MADS-box proteins, and ArgRII, a zinc cluster protein, contain putative DNA binding domains, alone they are unable to bind the arginine boxes in v itro, Using purified glutathione S-transferase fusion proteins, we demonstr ate that ArgRI and ArgRII1-180 or Mcm1 and ArgRII1-180 are able to reconsti tute an arginine-dependent binding activity in mobility shift analysis. Bin ding efficiency is enhanced when the three recombinant proteins are present simultaneously. At physiological concentration, the full-length ArgRII is required to fulfill its functions; however, when ArgRII is overexpressed, t he first 180 amino acids are sufficient to interact with ArgRI, Mcm1, and a rginine, leading to the formation of an ArgR-Mcm1-DNA complex. Several line s of evidence indicate that ArgRII is the sensor of the effector arginine a nd that the binding site of arginine would be the region downstream from th e zinc cluster, sharing some identity with the arginine binding domain of b acterial arginine repressors.