Figure 3.

RNA Gel Blot Analysis of NIT2 Expression, Intracellular Nitrate, and Ars Activity in D2R4 and SIR6 Strains.

Ammonium-grown cells were transferred to medium containing 8 mM NH₄Cl or 4 mM KNO₃ or to N-free medium for 1.5 h of incubation. Isolated poly(A) mRNA (10 μg) of the indicated strains and conditions was loaded onto the gel, and a 1-kb PstI-KpnI fragment from the pMN68 plasmid was used as a probe for NIT2 detection. Intracellular nitrate concentrations (expressed as nanomoles of nitrate per milligram of protein) and Ars activity (milliunits per milligram of protein) in these strains were determined. nd, not detectable.