Domain structure of BolA-like proteins from E. coli, S. cerevisiae, S. pombe, and H. sapiens. The protein names of members of the BolA1, BolA2, and BolA3 subfamilies are shown in red, blue, and cyan, respectively. E. coli YrbA is not grouped in any of these subfamilies based on phylogenic analysis (59). The BolA-like domain is shown as a green box, while predicted or known mitochondrial targeting signals are shown as pink boxes. The conserved histidines identified as Fe-S ligands in some family members are numbered and shown in yellow.