Title Organelle Targeting of Citrate Synthases in Saccharomyces cerevisiae
Author Lee, Heon Sik · Choi, Wan Sung¹ · Lee, Jeoung Sook¹ · Maeng, Pil Jae *
Address Department of Microbiology, College of Natural Sciences, Chungnam National University; ¹Department of Anatomy, School of Medicine, Gyeongsang National University
Bibliography Korean Journal of Microbiology, 32(6),558-564, 1994
Key Words Nonmitochondrial citrate synthase, mitochondrial citrate synthase, organelle targeting, Saccharomyces cerevisiae
Abstract The intracellular distribution and trafficking of the two citrate synthases, CS1 and CS2, has been investigated in Saccharomyces cerevisiae. Antibodies against CS1 and CS2 were generated from rabbit and mouse, respectively, and were used in tracing the localities of the isoenzymes by immunoelectron microscopy, which showed that CS1 is targeted to mitochondria and CS2 to peroxisomes. The subcellular localization of CS1 and CS2 was also examined by cell fractionation on a Nycodenz stepped gradient, and CS1 was found to be cosedimented with mitochondria, and CS2 with peroxisomes, respectively. The N-terminal sequence of CS1 was determined to be S-S-A-S-E-Q-T, which indicates that 37 N-terminal amino acids of the CS1 precursor are removed by the cleavage as R(35)-H-Y↓S(38) in the process of mitochondrial targeting and that this protein contains a R-3 type cleavage motif in the mitochondrial targeting signal. The N-terminal amino acid sequence of CS2 was revealed to be L-Q-S-N-S-S, which suggests that the 15 N-terminal amino acids are cut off from the CS2 precursor by the cleavage as A(13)-S-Y↓L(16) during its import into peroxisomes. It is thus quite noticeable that the N-terminal 15 amino acids of CS2 are cut off notwithstanding the presence of C-terminal peroxisomal targeting signal(PTS1), S-K-L, because none of the proteins containing PTS1 has been reported to have N-terminal sequence that are cleaved upon tranlocation ot the protein into peroxisomes yet.
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