Nucleotide Sequence and Genomic Structure of Duck Acyl-CoA Binding Protein/Diazepam-Binding Inhibitor: Co-Localization withS-Acyl Fatty Acid Synthase Thioesterase

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Abstract
A computer-aided homology search of the GenBank nucleotide database using the amino acid sequence of human acyl CoA-binding protein (ACBP)/diazepam-binding inhibitor (DBI)-endozepine as a probe revealed that a genomic fragment containing the gene encoding the mallard duck (Anas platyrhynchos) S-acyl fatty acid synthase thioesterase also contains sequences which encode the duck homolog of ACBP/DBI. The duck ACBP/DBI gene is positioned downstream of the thioesterase gene in a tail-to-tail orientation separated from the 3' end of the thioesterase gene by only several hundred nucleotides. Three exons were identified that have strong homology to the published cDNA sequences of human and bovine ACBP/DBI. These exons define all of the coding region except for the amino-terminal domain, which was subsequently cloned by polymerase chain reaction (PCR) amplification. The encoded amino acid sequence of the duck ACBP/DBI is 62-68% homologous to mammalian ACBP/DBI sequences. While the mammalian ACBP/DBI is expressed mainly in the liver, with smaller amounts in the brain and heart, mRNA transcripts of duck ACBP/DBI were detected only in the brain with no evidence for expression in the liver or heart. The close proximity of the genes for ACBP/DBI and S-acyl fatty acid synthase thioesterase raises the possibility of co-regulation of expression.