ArgRIIIp (Arg82p), together with ArgRIp (Arg80p), ArgRIIp (Arg81p) and Mcm1p, regulates the expression of arginine anabolic and catabolic genes. An argRIII mutant constitutively expresses five anabolic enzymes and is impaired in the induction of the synthesis of two catabolic enzymes. A genomic disruption of the ARGRIII gene not only leads to an argR phenotype, but also prevents cell growth at 37 degrees C. The disrupted strain is sterile especially in an alpha background and transcription of alpha- and a-specific genes (MF alpha 1 and STE2) is strongly reduced. By gel retardation assays we show that the binding of the Mcm1p present in a crude protein extract from an argRIII mutant strain to the P(PAL) sequence is impaired. Sporulation of alpha/a argRIII::URA3 homozygous diploids is also affected. Overexpression of Mcm1p in an argRIII-disrupted strain restores the mating competence of the strain, the ability to form a protein complex with P(PAL) DNA in vitro, and the regulation of arginine metabolism. However, overexpression of Mcm1p does not complement the sporulation deficiency of the argRIII-disrupted strain, nor does it complement its growth defect at 37 degrees C. Western blot analysis indicates that Mcm1p is less abundant in a strain devoid of ArgRIIIp than in wild type.