Fig. 9. Relationship of SmpB to other RNA-binding proteins. The structure of SmpB contains an embedded oligonucleotide binding (OB-fold); in this respect, SmpB is related to several other proteins associated with the translational apparatus. Ribosomal protein S17 and translation initiation factor IF1 are other members of the OB-fold family of proteins, and contain a five-stranded antiparallel β-sheet (shown in red), with the strands connected in a Greek-key topology. The N-terminal domain of aspartyl tRNA synthetase also contains the OB-fold within its structure, as does SmpB. The secondary structures of the aspartyl tRNA synthetase, S17, IF1 and SmpB are derived from PDB entries 1ASZ, 1RIP, 1AH9 and 1K8H, respectively.