HUMAN LIVER MITOCHONDRIAL CARNITINE PALMITOYLTRANSFERASE-I - CHARACTERIZATION OF ITS CDNA AND CHROMOSOMAL LOCALIZATION AND PARTIAL ANALYSISOF THE GENE

Using the cDNA for rat liver mitochondrial carnitine palmitoyltransfer ase I (CPT I; EC 2.3.1.21) as a probe, we isolated its counterpart as three overlapping clones from a human liver cDNA library. Both the nuc leotide sequence of the human cDNA and the predicted primary structure of the protein (773 aa) proved to be very similar to those of the rat enzyme (82% and 88% identity, respectively). The CPT I mRNA size was also found to be the same (approximate to 4.7 kb) in both species. Scr eening of a human genomic library with the newly obtained cDNA yielded a positive clone of approximate to 6.5 kb which, upon partial analysi s, was found to contain at least two complete exons linked by a 2,3-kb intron. Oligonucleotide primers specific to upstream and downstream r egions of one of the exon/intron junctions were tested in PCRs with DN A from a panel of somatic cell hybrids, each containing a single human chromosome. The results allowed unambiguous assignment of the human l iver CPT I gene to the q (long) arm of chromosome 11. Additional exper iments established that liver and fibroblasts express the same isoform of mitochondrial CPT I, legitimizing the use of fibroblast assays in the differential diagnosis of the ''muscle'' and ''hepatic'' forms of CPT deficiency. The data provide insights into the structure of a huma n CPT I isoform and its corresponding gene and establish unequivocally that CPT I and CPT II are distinct gene products. Availability of the human CPT I cDNA should open the way to an understanding of the genet ic basis of inherited CPT I deficiency syndromes, how the liver CPT I gene is regulated, and which tissues other than liver express this par ticular variant of the enzyme.