A malic enzyme probe detects cross-hybridizing sequences closely linked to loci encoding other metabolic enzymes

The cytoplasmic malic enzyme ( Mod-1) catalyzes the oxidative decarboxylation of malate: malate + NADP + ⇒ pyruvate + CO 2 + NADPH + H +. Using a cDNA clone of Mod-1 as a probe, two new DNA markers not at the Mod-1 locus (restriction fragment length polymorphisms, RFLP) were detected by Southern blot analysis that showed extensive homology to Mod-1 sequences. Linkage of each restriction fragment length polymorphism to loci other than Mod-1 was assessed using the BXD ( C57BL 6J × DBA 2J ) recombinant inbred strains and confirmed by backcrosses. One polymorphic site, designated D9Rti1, was found to be closely linked to the phosphoglucomutase ( Pgm-3) locus on Chromosome 9. The other hybridization site, designated D1Rti2, was closely linked to the isocitrate dehydrogenase ( Idh-1) locus on Chromosome 1. The data presented imply that Mod-1 homologous sequences are tightly linked to three different metabolic enzymes.