Molecular weight approximation of the D. radiodurans SSB protein oligomer. Gel filtration of the standards and SSB proteins were performed as described in the Methods section using a S-200 Sephacryl HR column. The protein standards β-amylase (200 kDa), alcohol dehydrogenase (150 kDa), bovine serum albumin (66 kDa), carbonic anhydrase (29 kDa), and cytochrome c (12.4 kDa) were used to calibrate the column as shown by open circles. The elution volume of blue dextran was used to calculate the void volume and the total volume of the column was known. The best-fit line was generated of the log Mr of the protein standards versus Kav of the standards. D. radiodurans SSB protein and E. coli SSB protein samples were injected onto the column in independent experiments and their elution volumes were used to calculate their Kav. The position of D. radiodurans SSB protein on the standard curve is indicated by a closed square and the position of E. coli SSB protein on the standard curve is indicated by an open square.