The acetyl-CoA (Ac-CoA) transporter (AT-1) is a multiple transmembrane protein in the endoplasmic reticulum. Ac-CoA is transported to the lumen of the Golgi apparatus, where it serves as the substrate of acetyltransferases that modify the sialyl residues of gangliosides and glycoproteins. The AT-1 gene, originally named ACATN (acetyl-CoA transporter), was cloned from human melanoma cells. Although homologs of this family of proteins have been identified in lower organisms, such as Escherichia coli, Drosophila melanogaster, and Caenorhabditis. elegans, currently only one member of this SLC33A1 family has been identified in humans. Thus, SLC33A1 proteins should be re-named ACATN1 or AT-1. Although acetylated gangliosides show a highly tissue-specific distribution, AT-1 is ubiquitously expressed. Phylogenetically, the AT-1 gene is highly conserved, suggesting that it is particularly significant. The precise physiological roles of this transporter protein, however, remain to be elucidated.