Fig. 1. Identification of the med-6 mutation. (A) The physical and genetic maps of the med-6 region. The yeast artificial chromosome (YAC) Y57E12 contained the med-6 gene. The cosmid gap within the YAC is indicated. The genetic deficiencies, sDf20 and sDf30, delete both unc-68 and odr-2, whereas the deficiency, nDf32, does not. Lethal mutations, let-322, let-339, let-343, let-404, let425, let-438 and let-468, which were mapped in that region, are shown. The map is not drawn to an exact scale. (B) Genomic structure of med-6 and the mutation identified in let-425. The med-6 gene contains three exons separated by two introns. The med-6 gene isolated from the homozygous let-425 animals contained a point mutation that changes C to T, causing a change in the amino acid residue from Arg to a stop codon. The numbers above the genomic structure are the amino acid numbers encoded by the gene.