|  | Class a: All alpha proteins [46456] (202 folds) | 
|  | Fold a.22: Histone-fold [47112] (1 superfamily) core: 3 helices; long middle helix is flanked at each end with shorter ones | 
|  | Superfamily a.22.1: Histone-fold [47113] (3 families)  | 
|  | Family a.22.1.1: Nucleosome core histones [47114] (4 proteins) form octamers composed of two copies of each of the four histones | 
|  | Protein Histone H4 [47125] (4 species) | 
|  | Species African clawed frog (Xenopus laevis) [TaxId:8355] [47127] (19 PDB entries) | 
Timeline for Species African clawed frog (Xenopus laevis) [TaxId:8355] from a.22.1.1 Histone H4: