Deletion mutagenesis of stem cell factor defines the C-terminal sequences essential for its biological activity

We constructed a series of murine stem cell factor (mSCF) cDNAs which were sequentially truncated at the 3' termini. The resultant six mutant cDNA encode N-terminal 183, 179, 162, 149, 142 and 133 amino acid residues of the mature mSCF protein fused to the heterogeneous C-terminal peptides derived from the linker sequences. Each mutant cDNA was transiently expressed in COS cells, and the cultured supernatant was assayed for its ability to support the growth of a human factor-dependent cell line, TF-1 and to enhance colony formation by murine hematopoietic progenitor cells. The results showed that as few as N-terminal 142 but not 133 amino acid residues of mSCF remained biologically active in vitro, suggesting that the region of 9 amino acids from Asp134 to Ser142 containing a Cys138-mediated disulfide bond may contribute to the C-terminal end of the active subdomain of mSCF.