Effect of mutations on structure and function for residues 140 to 157. A helical wheel presentation shows amino acids found in rHuEPO (closest to the circle). Arrows point to mutations (in boxes). RIA-9G8A immunoreactivity for each variant is shown in parentheses adjacent to the mutation. Shading indicates the effect of the mutation on in vitro bioactivity. Predicted buried and exposed surfaces are indicated.