Sequence alignment of SSB proteins. Gram-positive and Gram-negative bacteria: ssDNA binding and protein-protein interactions domains of SSB proteins from Gram-positive B. anthracis (SSB-BA), and Gram-negative E. coli (SSB-EC), Salmonella typhimurium (SSB-ST), Klebsiella pneumoniae (SSB-KP), Pseudomonas aeruginosa (SSB-PA) were aligned using ClustalW2 program. The color coding is as follows: red, basic; blue hydrophobic; green, hydrophilic; orange, neutral; pink, acidic; and light green, proline. Notations of the secondary structures in SSBBA are as defined by Murzin  with the β strands of the OB-fold labeled 1–5 (Light green box) and the α-helix (dark green box). Locations of the important hydrophobic tryptophans (in E. coli) are indicated by red up arrows. The residues in the monomer-monomer interface of the dimer in E. coli SSB sequence are indicated in yellow boxes. Changes of Gln77 →Leu and Gln111→Phe should destabilize dimer-dimer interaction important for the tetramer formation .