Phylogenetic analysis of the conserved catalytic domains of STKs. A phylogenetic tree based on the catalytic domains of cyanobacterial STKs was constructed as described in Methods. Strain names are as in Figure 1. Bootstrap values >50% are indicated on the branches. Additional domain names are also given following the gene names. STKs from subfamily cbSTKI-TM are marked in red and bold and those from cbSTKI-I are marked in red, bold, and italics. STKs with additional domains from cbSTKII are marked in bold and some major additional domains are marked in color: green WD40; blue DUF323; purple TPR; and magenta pentapeptide. Members of the family cbSTKIII family are highlighted in a cyan box. Archaeal and eukaryotic STK proteins are in yellow boxes.