Structure of the Canine Pancreatic Lipase Gene

Abstract

Identification of three overlapping clones in a canine genomic lambda phage library allowed us to determine a detailed restriction enzyme map of the primary transcriptional unit of the pancreatic lipase gene (15.5 kilobase pairs) as well as 15 and 6 kilobase pairs of 5'- and 3'-flanking regions, respectively. DNA sequence analysis provided the primary structure of (a) 1,345 nucleotides (nt) of 5'-flanking sequence including CAAT and TATA boxes at positions -112 and -35, respectively, and a class 2 glucocorticoid receptor binding sequence at position -97, (b) 13,127 out of approximately 15,500 nt of the transcriptional unit which is organized into 13 exon sequences, and (c) 1,270 nt of 3'-flanking sequence. Exon 1 encodes the entire 5'-nontranslated mRNA sequence; exon 2, the ATG initiation codon and the hydrophobic portion of the signal peptide; and exon 6, Ser154 which shows homology to the active Ser152 in the porcine enzyme. Comparison of the amino acid sequences of human lipoprotein lipase, rat hepatic lipase, and Drosophila yolk proteins 1, 2, and 3 with canine pancreatic lipase shows that the central region of highest homology (encoded by exons 6-8 in the dog gene) contains four highly conserved subregions which may play a critical role in enzyme-substrate and protein-ligand binding for lipases and yolk proteins, respectively. Comparison of the sequences of 10 lipases from prokaryotes and eukaryotes identifies a 9-residue consensus sequence surrounding the active serine which includes the previously identified sequence Gly-X-Ser-X-Gly. The hydrophobic nature of this sequence in the 10 lipases contrasts with the hydrophilic nature of the corresponding sequences in serine proteases and thus defines an active site serine consensus sequence specific for lipases. An analysis of 5'- and 3'-flanking and intron 1-4 sequences in transient expression studies with AR4-2J and 266-6 cells was unable to reveal tissue-specific promoter or enhancer sequences.