Demonstration in mouse of X-ray induced deletions for a known enzyme structural locus

Abstract

THE known lethal alleles at the albino locus of mice are radiation-induced and cause prenatal or early neonatal death. Four alleles expressed in the homozygous newborn as absence of pigment and early neonatal death (c^14COS, c^112K, c^65K, and c^3H) were found to cause hypoglycaemia and deficiency of glucose-6-phosphatase and other enzymes^1–3. Two additional radiation-induced alleles (c^6H and c^25H) act as early embryonic lethals. Complementation tests between these lethal-albino alleles suggested that all six mutations could be deficiencies for genetic material other than just the albino locus¹. Since X rays are known to produce small deletions4,5, all six of these mutations have been tested with various closely linked genes using the standard deletion mapping procedure. Unfortunately, the two most closely linked genes to c, taupe (tp) and shaker-1 (sh-1) (order with centi-Morgans (cM) distance, tp – 2 – c – 4 – sh-1), seemed not to have been deleted in any of the six lethal-albino mutations^2,6. Recently, the gene mitochondrial malic enzyme (Mod-2) that codes for electrophoretic variants of mitochondrial malic enzyme (MOD-2: EC 1.1.1.40, L-malate: NADP oxidoreductase, de-carboyxlating) was shown to reside in chromosome 7 one cM from c between c and sh-1 (ref. 7 and E. M. E. and D. L. Coleman, in preparation). We present evidence here showing that two of these mutations (c^6H and c^25H), but not the C^14cos mutation, are deletions that extend into the Mod-2 locus.