Transport of solutes and polypeptides across membranes is an essential process for every cell. In the past, much focus has been placed on helical transporters. Recently, the beta-barrel-shaped transporters have also attracted some attention. The members of this family are found in the outer bacterial membrane and the outer membrane of endosymbiotically derived organelles. Here we analyze the features and the evolutionary development of a specified translocator family, namely the beta-barrel-shaped polypeptide-transporters. We identified sequence motifs, which characterize all transporters of this family, as well as motifs specific for a certain subgroup of proteins of this class. The general motifs are related to the structural composition of the pores. Further analysis revealed a defined distance of two motifs to the C-terminal portion of the proteins. Furthermore, the evolutionary relationship of the proteins and the motifs are discussed.