Localization and intron usage analysis of the human CPT1B gene for muscle type carnitine palmitoyltransferase I

We isolated and sequenced cDNA and genomic DNA fragments of the human CPTIB gene, encoding muscle type carnitine palmitoyltransferase I. A recombinant P1 phage containing CPTIB was mapped to chromosome 22qter by fluorescent in situ hybridization. This finding supports the concept that 'liver type' and 'muscle type' isoforms of CPT I are encoded by different loci at separate chromosomal positions. Analysis of CPTIB cDNA sequences revealed the presence of an untranslated 5' exon and differential processing of introns 13 and 19. The alternative splicing of intron 13 causes an in-frame deletion leading to a 10 amino acid residues smaller protein. Using different splice acceptor sites, intron 19 is spliced in the majority of cases, but 4 out of 14 sequenced CPTIB 3' cDNA clones contain part of intron 19 instead of exon 20. We found that differential polyadenylation is the mechanism behind the existence of these alternative 3' CPTIB mRNA forms.