An allelic series of mutations in the kit ligand gene of mice. I. Identification of point mutations in seven ethylnitrosourea-induced Kitl(Steel) alleles.

An allelic series of mutations is an extremely valuable genetic resource for understanding gene function. Here we describe eight mutant alleles at the Steel (Sl) locus of mice that were induced with N-ethyl-N-nitrosourea (ENU). The product of the Sl locus is Kit ligand (or Kitl; also known as mast cell growth factor, stem cell factor, and Steel factor), which is a member of the helical cytokine superfamily and is the ligand for the Kit receptor tyrosine kinase. Seven of the eight ENU-induced Kitl(Sl) alleles, of which five cause missense mutations, one causes a nonsense mutation and exon skipping, and one affects a splice site, were found to contain point mutations in Kitl. Interestingly, each of the five missense mutations affects residues that are within, or very near, conserved alpha-helical domains of Kitl. These ENU-induced mutants should provide important information on structural requirements for function of Kitl and other helical cytokines.