FIG. 4.

Effects of removal of Put3p, Gln3p, and Nil1p on nitrogen regulation of PUT1. (A) Nitrogen regulation of PUT1 under noninducing conditions. (B) Expression of PUT1 with proline as the sole source of nitrogen. The strains listed in Fig. 3 were grown in minimal medium containing glutamine (Gln, 0.1%), ammonia (Amm, 0.2%), glutamate (Glt, 0.1%), GABA (0.1%), or proline (Pro, 0.1%) as the nitrogen source. Extracts were made and assayed for β-galactosidase activity. Results are the average of two to five independent measurements with variations as indicated. WT, wild type.