Wild-type and mutant KITL proteins (membrane-bound is indicated by MB; precursor, Pre; and soluble, S forms). The mRNAs encoding each form are described briefly in the text. The original reference describing each mutation is as follows: Kitl^Sl-39R and Kitl^Sl-36R (Rajaraman et al, 2002a), Kitl^Sl-17H (Brannan et al, 1992), and Kitl^Sl-d (Brannan et al, 1991; Flanagan et al, 1991). For each mutant, MB*, Pre*, and S* refer to KITL proteins that have altered sequences. For wild-type and mutant proteins, the following symbols are used: solid black rectangles are the 4 -helical domains; the light grey rectangle is the alternately spliced exon 6 that contains the proteolytic cleavage site, shown as a jagged line; black rectangles with dots are transmembrane domains, the ovals and numbers to the right of each protein are the sites of N-linked glycosylation sites, and the amino acid number (with 1 at the N-terminus), respectively. For KITL^Sl-39R, the white asterisk indicates the position of the S122F missense mutation. For KITL^Sl-17H, KITL^Sl-d, and KITL^Sl-136R, the numbers corresponding to the C-terminal KITL sequence plus the numbers of out-of-frame residues are shown with outof-frame sequences indicated as cross-hatched rectangles.