Crystal structure of E. coli SspB (ribbon) in complex with AANDENYALAA tag peptide (stick, only the AANDENYA portion was modeled) from Song and Eck (2003) Molec. Cell 12:75. Only the top part of the second unit of the dimer is shown. SspB has a fold found in the Sm-family of RNA binding proteins, although any RNA-binding properties have not been characterized.