Swine cytosolic malic enzyme: cDNA cloning, sequencing, and localization.

A highly significant genetic association has been found between some alleles of the swine Major Histocompatibility Complex SLA (Swine Leukocyte Antigen genetic complex) and the cytosolic malic enzymatic activity level in muscles. The aim of this study was to find out whether this genetic association was due to a close linkage of the SLA region and the gene coding for the enzyme. Since no swine cytosolic malic enzyme sequence (ME1) was available, we isolated several overlapping fragments that spanned the almost entire malic enzyme transcript both by screening of a swine cDNA library and by RT-PCR. The results indicated the existence of two transcripts of 2. 0 and 3.1 kb, which probably correspond to two alternative forms of one gene. The sequence of the transcript was highly similar to the other published mammalian cytosolic NADP+-dependent malic enzyme cDNA, especially within the four functional domains. Two major bands at 3.7 and 2.4 kb were detected on Northern blots containing the RNA from 25 tissues from fetuses and adult pigs. A high expression level was found in the adrenal gland, muscle, liver, and peripheral nerves. The analysis of malic enzyme RFLPs in five SLA informative families revealed an independent segregation of the ME1 gene from the SLA region. In situ hybridization results localized the cytosolic malic enzyme on the swine Chromosome (Chr) 1p1.2, except that the association between SLA and the malic enzyme activity level was due to a physical genetic linkage. Thus, the mechanisms underlying this association remain to be elucidated.