The ethanol-inducible YAT1 gene from yeast encodes a presumptive mitochondrial outer carnitine acetyltransferase.

Abstract

The gene YAT1 from Saccharomyces cerevisiae encodes a protein of 688 amino acids which displays significant sequence similarity to vertebrate L-carnitine acyltransferases and yeast inner mitochondrial L-carnitine acetyltransferase. Steady state levels of the respective mRNA are low during growth on glucose or galactose, derepressed on glycerol, and significantly induced when ethanol or acetate are the only carbon sources. The YAT1 promotor region confers the identical carbon source dependence also on the expression of beta-galactosidase when cloned 5' to the Escherichia coli lacZ-coding region. An antiserum directed against a beta-galactosidase/Yat1p fusion protein recognizes a protein of 78-kDa molecular mass in the mitochondrial fraction from yeast. In vitro translated Yat1p, which lacks a cleavable presequence, binds to mitochondria in a protease-sensitive location in a standard in vitro import assay. Deletion of the single copy gene in a haploid yeast strain yields no obvious phenotype with any carbon source. Carnitine acetyltransferase activities of intact mitochondria from a YAT1 deletion mutant are slightly lower than wild type, but are approximately alike in lysed mitochondria from mutant and control cells. Thus, the novel gene is nonessential and likely to code for a minor mitochondrial outer carnitine acetyltransferase.