Phylogenetic analysis of STK catalytic domains, GAF and HikA additional domains. Phylogenetic trees were constructed from the amino acid sequences of the catalytic, GAF and HikA domains of dual protein kinases, as described in Methods. Branches with bootstrap support below 50% have been collapsed. Four proteins (Anabaena PCC7120 _All3691, A.variabilis _3596, N. punctiforme _02004756 and N. punctiforme _02004457) have two GAF domains and one (N. punctiforme _02004457) has three. The strain abbreviations are as in Figure 1. Orthologous genes, conserved in three strains, were marked in yellow box. Members in cyan boxes are possible examples of domain shuffling.