Amphipathic α-helical amino acid tracts punctuated by proline-induced turns. CDC16, CDC23, and CDC27 of yeast and their homologs in other eukaryotes all contain tandem repeated ∼34-residues. Such motifs exist in more than 100 proteins and may control mitosis and RNA synthesis in the cells.  APC,  CDCs; Wendt KS et al 2001 Nature Struct Biol 8:784; Cortajarena AL, Regan L 2006 Protein Sci 15:1193.