G-CSF–induced colony formation of Gcsfr^-/- bone marrow cells transduced with either wild-type G-CSF-R or G-CSF-R_785Lys. Colonies were grown in the presence of 100 ng/mL G-CSF. Percentages of colony numbers as compared with wild-type G-CSF-R from triplicate colony dishes of 4 independent experiments are shown (mean ± SE). Differences between wild-type G-CSF-R and G-CSF-R_785Lys are highly significant (Student t test, P < .001).