THE ETHANOL-INDUCIBLE YAT1 GENE FROM YEAST ENCODES A PRESUMPTIVE MITOCHONDRIAL OUTER CARNITINE ACETYLTRANSFERASE

The gene YAT1 from Saccharomyces cerevisiae encodes a protein of 688 a mino acids which displays significant sequence similarity to vertebrat e L-carnitine acyltransferases and yeast inner mitochondrial L-carniti ne acetyltransferase. Steady state levels of the respective mRNA are l ow during growth on glucose or galactose, derepressed on glycerol, and significantly induced when ethanol or acetate are the only carbon sou rces. The YAT1 promotor region confers the identical carbon source dep endence also on the expression of beta-galactosidase when cloned 5' to the Escherichia coli lacZ-coding region. An antiserum directed agains t 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 mitoc hondria in a protease-sensitive location in a standard in vitro import assay. Deletion of the single copy gene in a haploid yeast strain yie lds no obvious phenotype with any carbon source. Carnitine acetyltrans ferase activities of intact mitochondria from a YAT1 deletion mutant a re slightly lower than wild type, but are approximately alike in lysed mitochondria from mutant and control cells. Thus, the novel gene is n onessential and likely to code for a minor mitochondial outer carnitin e acetyltransferase.