30 and 16.58 kDa, respectively. They are the smallest prokaryotic SSB proteins so far identified (E. coli SSB with N-terminal methionine

consists of 178 amino acid residues). Analysis of the primary structures by RPS-BLAST [22] revealed the presence of two distinctive regions: one putative OB-fold domain selleck products (from amino acid 1-120) and one C-terminal domain that contains five conserved DEPPF terminal amino acids, which are common in all known bacterial SSB proteins. Figure 1 shows an alignment of amino acid sequences of T. maritima, T. neapolitana, Thermoanaerobacter tengcongensis, Sulfolobus solfataricus and E. coli SSB proteins containing one OB-fold domain for monomer, and T. aquaticus, T. thermophilus, D. geothermalis and D. radiopugnans

thermostable SSB proteins containing two OB-fold domains for monomer. The similarity between the amino acid sequences of Thermotoga SSBs is very high: 90% identity and 95% similarity. Surprisingly, both Thermotoga SSBs had a quite low sequence similarity to Escherichia coli SSB (TmaSSB has 36% identity and 55% similarity, TneSSB has 35% identity and 56% similarity), whereas the similarity to Thermoanaerobacter tengcongensis SSB3 was higher (63 and 64% similarity; 40 and 42% identity for TmaSSB and TneSSB, respectively). Figure 1 A: Multiple amino acid sequence alignment of SSB proteins. Alignment was performed by see more dividing amino acids into six similarity groups: group 1, V, L, I and M; group 2, W, F and Y; group 3, E and

selleck compound D; group 4, K and R; group 5, Q and D; group 6, S and T. White fonts on black boxes denote 100% identity; white fonts on grey boxes show <80% similarity; black fonts on grey boxes show <60% similarity. B: Dendogram of SSB proteins. Abbreviations: Tma, T. maritima strain MSB8; Tne, T. neapolitana; EcoK12, E. coli K12; TteSSB2, TteSSB3, T. tengcongensis strain MB4; Taq, T. aquaticus strain YT1; Tth, T. thermophilus strain HB8; Dge, D. geothermalis; Drp, D. radiopugnans strain R1; Sso, Florfenicol S. solfataricus P2; N, N-terminal ssDNA-binding domain; C, C-terminal ssDNA-binding domain. Expression and purification of the recombinant TmaSSB and TneSSB proteins Using the recombinant plasmid pETSSBTma or pETSSBTne, the expression of inducible proteins with the predicted size was excellent (Figure 2, lanes 1 and 5). Both proteins were expressed in a soluble form in the cytosol. Heat treatment resulted in considerably less contamination by the host proteins (Figure 2, lanes 2 and 6). The E. coli overexpression system used in this study produced about 40 and 35 mg of purified TmaSSB and TneSSB protein, respectively, from 1 l of induced culture. The purity of the protein preparations was about 99% (Figure 2, lanes 4 and 8). Figure 2 Expression and purification of the Tma SSB and Tne SSB. Proteins expression were obtained from the pET30Ek/LIC vector in BL(DE3)pLysS E. coli cells. Proteins were examined on 15% SDS-polyacrylamide gel.