Research Service, Department of Veterans Affairs Medical Center, Dallas, Texas.
Previously we described the coding region of bovine heart Fructose 6-P,2-kinase:Fructose 2,6-bisphosphatase as determined from cDNA. We have isolated several overlapping clones and determined the DNAs which encode the entire mRNA of bovine heart bifunctional enzyme, including the 5'- and 3'-noncoding regions. the exon-intron structure of the 27-kb gene was determined and shown to consist of 16 exons. There are one primary and two secondary transcription initiation sites with the coding region beginning at exon 2. Exons 3-7 encode the Fructose 6-P,2-kinase domain, and exons 9-14 encode the Fructose 2,6-biphosphatase domain. Exon 15 is a unique exon for the heart type isozyme and contains the phosphorylation sites for protein kinases A and C. Alternative splicing of this exon accounts for the expression of two heart type isozymes in cardiac muscle. Exon 16 (also unique), 1820 bp long and located 7 kb downstream of exon 15, encodes the short C-terminus of the enzyme and is completely different from that of the rat heart bifunctional enzyme gene.