Multiple alignment of the amino acid sequences predicted to be encoded by the M. pneumoniae MPN229 , M. genitalium MG091, U. parvum ssb, and E. coli ssb genes. The amino acid motifs that are characteristic for the OB DNA-binding fold are indicated by the open boxes below the aligned sequences . The asterisk above Y44 of the M. pneumoniae sequence indicates the position of a Trp residue (W55) in E. coli SSB that was shown to play a role in DNA-binding. The other two asterisks indicate conserved arginine (R) and lysine (K) residues (R46 and K52, respectively, in the M. pneumoniae sequence); for E. coli SSB these residues were shown to be oriented toward the DNA binding cleft . The multiple aligment was performed using Clustal W http://www.ebi.ac.uk/Tools/clustalw/index.html. The program BOXSHADE 3.21 http://www.ch.embnet.org/software/BOX_form.html was used to generate white letters on black boxes (for residues that are identical in at least two out of four sequences) and white letters on grey boxes (for residues that are similar in at least two out of four sequences).