FIG. 9.
The cysteine residues in the extracellular domain of a constitutively active Sf-Stk are required for Epoind BFU-E colony formation. (A) 293 cells were transfected with gp55 and myc-tagged wild-type or mutated Sf-Stk. Cell lysates were immunoprecipitated with anti-tyrosine phosphorylation antibody and blotted with anti-myc antibody. (B) 293 cells were transfected with wild-type or mutated MSCV-myc-Sf-Stk and pEco. At 48 h posttransfection, viral supernatants were collected and incubated overnight with bone marrow cells of C57BL/6 mice. The infected bone marrow cells were plated in methylcellulose medium containing IL-3 (2.5 ng/ml) or incubated with FVP on ice for 1 h prior to plating in methylcellulose medium containing IL-3 (2.5 ng/ml). On day 5, BFU-E colonies were stained with acid-benzidine and counted. *, P < 0.01. Error bars indicate standard deviations.