Variations in amino acid content of different secondary structural regions. The differences in the contributions of individual amino acids to secondary structural regions in orthologous proteins from (a) S. ruber and P. luteolum (set I), (b) H. marismortui chromosome I and P. putida (set II), (c) H. marismortui chromosome I and M. thermophila (set III) and (d) N. pharaonis and methanogenic archaeon (set IV). The differences were derived as D = (Frequency of halophile amino acid residue - Frequency of non-halophile amino acid residue). Black, grey and red bars indicate helix, sheet and coil regions, respectively, and asterisks indicates significant differences at p < 10-2. Organism abbreviations are listed in Table 1.