Architecture and evolution of operons containing form 1A RubisCO from proteobacteria and α-cyanobacteria including the Paulinella chromatophore. Gene arrangements from selected taxa (see arrowheads in Figure 3) are plotted against a simplified phylogram based on RubisCO amino acid sequences. Four major types of gene arrangements can be distinguished (for details, see text). The operon of Paulinella is member of the α-cyano-cso-type, which is derived from the ancestral cso-type present in proteobacteria, providing evidence for a HGT of the complete operon. Homologous genes share the same colour. Abbreviations: Carboxysomal shell proteins 1, 2, 3 (csoS1, 2, 3); RubisCO large and small subunit (rbcL, rbcS = cbbL, cbbS); carboxysomal peptides A, B (pepA, pepB); bacterioferritin (bfr); LysR-type transcriptional activator (cbbR); putative RubisCO activation proteins (cbbQ, cbbO); hypothetical proteins (hypo). Dotted lines indicate that no data are available.