Figure 5.

Evolution of A. variabilis’ heterocyst-specific ORF3 protein and higher plant chloroplasts’ GAPDH subunit GAPB. (A) Amino acid sequences of the hypothetical proteins, ORF4 and ORF3, from A. variabilis, most probably involved in heterocyst-specific N₂ fixation, and the sequence of the C-terminal extension of pea chloroplast GAPDH subunit GAPB, involved in photosynthetic CO₂ fixation, are aligned with the peptide sequences of CP12 from Synechocystis and pea. Peptide loop-forming conserved cysteine residues are boxed. (B) Graphical illustration of the proposed gene fusion events. Homologous sequences given in A are presented by identically shadowed boxes. CP12 cysteine residues are indicated by a single or double c.