Significant effect of the N-terminal region of the mitochondrial ADP/ATP carrier on its efficient expression in yeast mitochondria.

The low-level expression of the bovine heart mitochondrial ADP/ATP carrier (bovine type 1 ADP/ATP carrier (bAAC1)) in the yeast mitochondrial membrane is significantly improved by replacement of its N-terminal region with corresponding regions of the yeast type 1 and 2 carriers (yAAC1 and yAAC2) (Hashimoto, M., Shinohara, Y., Majima, E., Hatanaka, T., Yamazaki, N., and Terada, H. (1999) Biochim. Biophys. Acta 1409, 113--124). To understand why the bAAC1 chimeras were highly expressed in yeast mitochondria, we examined the effects of the length and sequence of the N-terminal region extending into the cytosol on the expression of bAAC1 and yAAC2 derivatives in yeast mitochondria. For this, their N-terminal regions were replaced with peptide fragments of various lengths and sequences derived from those of bAAC1, yAAC1, and yAAC2. We found that a specific amino acid sequence and a definite length of the N-terminal region of yAAC2 were required for high expression of bAAC1 and yAAC2 in yeast mitochondria. We also examined the steady-state transcript levels and expression of these derivatives in whole yeast cells. Based on our results, we discuss the role of the N-terminal region in efficient expression of bAAC1 and yAAC2 in yeast mitochondria.