Fig 3. Arginine represses NIA1 expression by acting within the CYG56 pathway.

Arylsulfatase (ARS) activity in the presence or absence of arginine was determined in the parental strain 704, and in the cyg56 and non1 mutants. NIA1::ARS activity was measured after three and four days of growth on solid medium supplied with 4 mM NO₃^– and with different concentrations of arginine as indicated on the figure. (A). Growth control showing that the cells grew normally in the different conditions used in this experiment. (B). ARS test after three days of growth. (C). ARS test after four days of growth. The three strains 704, cyg56 and non1 bear a copy of the ARS gene fused to the NIA1 promoter. ARS activity in the presence of arginine reveals that the NIA1 promoter is not fully sensitive to arginine-mediated repression.