FIG. 3.

Loss of Arg80 function resulting from the swapping of residues in the MADS box domain of Arg80 with the corresponding residues in Mcm1. Strain 02463dΔARG80 was transformed with the listed plasmids, and Arg80 function was determined by a growth test on M.ornithine as the sole nitrogen source and by assays of OTCase and arginase activities after growth on M.ammonia with or without arginine (1 mg/ml). For growth on ornithine, +++ indicates growth at levels similar to that of a wild-type strain, ++ indicates a slight growth reduction, and −− indicates residual growth of an arg80 deletion strain. For repression of OTCase and induction of arginase, +++ indicates the same repression level (fourfold) and induction level (10-fold) as those obtained with a wild-type Arg80 protein, ++ indicates a twofold repression level and a four- to fivefold induction level, + indicates a 1.5-fold repression level and two- to threefold induction level, and - indicates an absence of induction or repression. The predicted secondary structure of the MADS box domain of Arg80 and its amino acid sequence are indicated. The smaller letters indicate the amino acids of Arg80 and Mcm1 that are identical, and the larger letters indicate the nonconserved residues. In each line, the residues indicate the amino acids of Mcm1 that were used to replace the corresponding amino acids in Arg80.