Fig. 2. The membrane association of P_II is affected by the cellular nitrogen status. Membrane fractions of strain GT1000 (pMM280) [ΔglnK amtB (glnK amtB3)] were subjected to SDS–PAGE followed by western blotting using either an anti-His tag antibody to detect AmtB-His₆ (A; B is a non-specific cross-reaction) or an anti-P_II antibody to detect P_II (C). Extracts were prepared from cells grown in nitrogen-limiting conditions (–N) and 15 min after ammonia shock (AS). The control lane contained 0.3 µg of purified E.coli GlnK. Molecular weight markers (Sigma, wide molecular weight standards M6539) run on the same 12.5% SDS–polyacrylamide gel are shown for calibration.