Clustal X alignment of GS2a and GS2b deduced amino acid sequences. Residues fully conserved (*), highly conserved (:), poorly conserved (.) and not conserved (). The transit peptide is represented in gray and was predicted by analogy with the GS2 from pea . Black boxes outline potential modified residues affecting GS2b activity. The black dots indicate two cysteine residues which are conserved in all plastid located isoenzymes . I-IV-identifies the conserved segments between GS proteins defined by Eisenberg et al. .