Analysis of the catalytic functionality of GS2b. A. Complementation analysis of an E. coli glnA mutant expressing either GS2b or GS2a plant cDNAs. The plant cDNA corresponding to the coding sequences, without the predicted transit peptide were introduced into pTrc99A. Controls were transformed with the empty plasmid. Bacteria were grown on Minimal Medium (M9) agar plates with (+GLN) and without (-GLN) a glutamine supplement (0.25 mg mL-1). B. Western blot analysis of E. coli glnA extracts expressing recombinant GS2a or GS2b mature proteins probed with anti-GS antibody. C. GS activity assays of E.coli glnA- extracts expressing either GS2a or GS2b mature proteins. Results represent the mean of three independent experiments.