Peroxisomal and mitochondrial carnitine acetyltransferases of Saccharomyces cerevisiae are encoded by a single gene.

Abstract

Carnitine acetyltransferase (CAT) is present in mitochondria and peroxisomes of oleate‐grown Saccharomyces cerevisiae. Both proteins are encoded by the same gene, YCAT, which encodes a protein with a mitochondrial targeting signal (MTS) at the N‐terminus, and a peroxisomal targeting signal type 1 (PTS‐1) at the C‐terminus. Deletion of both motifs revealed the presence of an additional internal targeting sequence. Import of CAT via this internal signal was shown to be dependent on PAS10, a protein which is required for the import of PTS‐1 containing proteins. An interaction of PAS10 with this internal targeting signal was demonstrated using the yeast two‐hybrid technique. Expression of the YCAT gene behind a heterologous promoter resulted in loss of peroxisomal targeting, indicating that differential targeting is controlled at transcriptional or translational level. Determination of the 5′‐ends of YCAT mRNAs revealed that YCAT transcripts initiating after the first AUG were present in oleate‐grown cells. These transcripts were virtually absent in acetate‐ or glycerol‐grown cells. We propose that in response to oleate, shorter transcripts are produced from which the peroxisomal form of CAT is translated, resulting in a CAT protein without a MTS, which can be targeted to peroxisomes.

A sequence resembling a peroxisomal targeting sequence directs the interaction between the tetratricopeptide repeats of Ssn6 and the homeodomain of α2

“…An example of this type of signal prioritization is seen for the protein carnitine-acetyltransferase, the Cat2 gene product in S. cerevisiae, which contains signals for both mitochondrial and peroxisomal import. Only when Cat2 is missing the mitochondrial-targeting signal, generated through the use of an alternative initiation codon, is it imported into the peroxisome (26).…”

The activity of the glyoxylate cycle in peroxisomes of Candida albicans depends on a functional β-oxidation pathway: evidence for reduced metabolite transport across the peroxisomal membrane

“…Proteins delivered to the peroxisome via the Pex7p receptor possess a PTS2, a bipartite amino acid motif with the consensus sequence R/ K-L/V/I-x 5 -H/Q-L/A (Gietl et al, 1994;Glover et al, 1994b) present in the amino terminus of these proteins. A number of proteins can be imported into peroxisomes independent of a recognizable PTS1 or PTS2 (Elgersma et al, 1995;Klein et al, 2002;Ozimek et al, 2006;Small et al, 1988). Subsequent studies have shown that, although the targeting signal is as yet not characterized, Pex5p mediates the peroxisomal sorting of these proteins (Elgersma et al, 1995;Klein et al, 2002;Ozimek et al, 2006).…”

“…A number of proteins can be imported into peroxisomes independent of a recognizable PTS1 or PTS2 (Elgersma et al, 1995;Klein et al, 2002;Ozimek et al, 2006;Small et al, 1988). Subsequent studies have shown that, although the targeting signal is as yet not characterized, Pex5p mediates the peroxisomal sorting of these proteins (Elgersma et al, 1995;Klein et al, 2002;Ozimek et al, 2006). Finally, some proteins can reach the organelle by association with another subunit or protein that possesses a functional targeting signal, a process referred to as 'piggy backing' (Glover et al, 1994a;McNew & Goodman, 1994;Yang et al, 2001).…”

Molecular Mechanisms and Physiological Significance of Organelle Interactions and Cooperation

“…Protein variants that encode targeting signals at the opposite ends of the protein probably necessitate the omission of the N-terminal targeting signal to disclose a functional PTS1 (lower panel). Thus, the two protein variants should differ in the absence or presence of the N-terminal targeting signal, which can be achieved by the omission of the N-terminal part of the protein sequence either by alternative translation initiation or leaky ribosome scanning (Elgersma et al, 1995;Wamboldt et al, 2009), next to the abovementioned mechanisms of alternative splicing and alternative transcription initiation (Ast et al, 2013).…”