Conserved domains and sites in cyanobacterial STKs according to Hanks and Hunter. A total of 32 sequences were used in the alignment of cyanobacterial STKs: 12 sequences in purple were selected to cover the diversity of species and structural characteristics; 6 sequences in red are of proteins reported to possess phosphorylation or autophosphorylation activity; 5 sequences in yellow were not originally annotated as protein kinases or Serine/Threonine Protein Kinases; and 9 sequences in green were those showing some deviations from the canonical domains of Hanks and Hunter . Each sequence is denoted by the species name followed by the gene names. The 12 conserved subdomains are indicated by Roman numerals according to Hanks and Hunter. Highly conserved eukaryotic and cyanobacteria-specific amino-acid residues are indicated above and below the alignment sequences respectively, using the single-letter amino-acid classes of Hanks and Hunter. Symbols, used to denote the various features according to Hanks and Hunter, are as follows: uppercase letters, universally conserved amino acid residues; lowercase letters, highly conserved amino acid residues; o, positions conserving non-polar residues; *, positions conserving polar residues; +, positions conserving small residues with near neutral polarity; and -, positions within a subdomain with no pattern of conserved amino acids. The number in parentheses preceding each sequence refers to the number of amino acid residues preceeding the sequence shown.