Molecular cloning of the gene for the yeast homolog (ACB) of diazepam binding inhibitor/endozepine/acyl-CoA-binding protein

Abstract

Diazepam binding inhibitor (DBI)/endozepine (EP)/acyl-CoA-binding protein (ACBP) is a small, highly conserved protein which has been independently isolated and characterized from different species using several different biological systems. To further investigate the structural and functional properties of this protein, we have cloned the homologous gene for DBI/EP/ACBP from the budding yeast Saccharomyces cerevisiae. The yeast gene contains no introns and encodes a polypeptide of 87 amino acids (including the initiating methionine), identical in length to the human gene product with 48% conservation of amino acid residues. The most highly conserved domain consists of 7 contiguous residues which are identical in all known protein species from yeast, birds, and mammals. This domain has previously been shown to constitute the hydrophobic binding site on DBI/EP/ACBP for acyl-CoA esters and is located within the second helical region of the molecule. Major and minor mRNA species of approximately 520 and 740 nucleotides, respectively, were detected in exponentially growing yeast. Sequences similar to those implicated in the regulation of fatty acid synthesis and beta-oxidation in yeast were detected in the promoter region of the gene. The presence of a highly conserved DBI/EP/ACBP gene in a primitive organism such as yeast provides support for the basic biological role of DBI/EP/ACBP as an acyl-CoA-binding protein and suggests that many of the biological functions attributed to it in higher organisms may result from its ability to interact with acyl-CoA. Hence, we have designated the yeast gene as ACB, for acyl-CoA-binding protein.