Effect of mutant rhCDD on mouse bone marrow GM-CFC. Thymidine (10^-4 mol/L) was added to all culture plates in the GM-CFC assay. The colonies (≥50 cells) were counted after 7 days in culture with 10% CM 5637 as stimulator. Mean values ± SD are given as percent of controls. Symbols: CDD truncated 12 amino acids from the C-terminus (□), Mutant E67D (•), Mutant E67Q (▵), Mutant E67A (▴), rhCDD (○), and extract from E coli BL21 transformed by the vector (pT7-SC) (▪).