The carboxyl-terminal tripeptide Ala-Lys-Ile is essential for targeting Candida tropicalis trifunctional enzyme to yeast peroxisomes

The gene encoding Candida tropicalis peroxisomal trifunctional enzyme, hydratase-dehydrogenase-epimerase (HDE), was expressed in both Candida albicans and Saccharomyces cerevisiae. The cellular location of HDE was determined by subcellular fractionation followed by Western blot analysis of peroxisomal and cytosolic fractions using antiserum specific for HDE. HDE was found to be exclusively targeted to and imported into peroxisomes in both heterologous expression systems. Deletion and mutational analyses were used to determine the regions within HDE which are essential for its targeting to peroxisomes. Deletion of a carboxyl-terminal tripeptide Ala-Lys-Ile completely abolished targeting of HDE to peroxisomes, whereas large internal deletions of HDE (amino acids 38-353 or 395-731) had no effect on HDE targeting to peroxisomes in either yeast. This tripeptide is similar to, but distinct from, other tripeptide peroxisomal targeting sequences (PTSs) as identified in peroxisomal firefly luciferase and four mammalian peroxisomal proteins. Substitutions within the carboxyl-terminal tripeptide (Ala----Gly and Lys----Gln) supported targeting of HDE to peroxisomes of C. albicans but not of S. cerevisiae. This is the first detailed analysis of the peroxisomal targeting signal in a yeast peroxisomal protein.

Incorporation of 7-deaza dGTP during the amplification step in the polymerase chain reaction procedure improves subsequent DNA sequencing

An improved method for sequencing human genomic DNA amplified by the polymerase chain reaction (PCR) procedure is described. The portion of the genome investigated is the 383 nucleotide-long exon 2 of the human antithrombin III gene. Incorporation of the analogue of dGTP, 7-deaza-2'-deoxyguanosine-5'-triphosphate, during the amplification of exon 2 by PCR allowed for the elimination of recurrent artifacts obtained during sequencing of the amplified DNA by the dideoxyribonucleotide chain termination method.

The primary structure of a peroxisomal fatty acyl-CoA oxidase from the yeast Candida tropicalis pK233

We report the isolation and nucleotide (nt) sequence determination of a gene encoding peroxisomal fatty acyl-CoA oxidase (AOx) from the yeast Candida tropicalis pK233. The AOx gene contains no intervening sequences and has a single open reading frame of 2127 nt encoding a protein of 708 amino acids (aa), not including the initiator methionine. The Mr of the protein is 79,155. Codon utilization in the gene is not random, with 87.4% of the aa specified by 25 principal codons. The principal codons used in the expression of AOx in C. tropicalis are similar to those used in highly expressed genes of Saccharomyces cerevisiae. The AOx protein shows a 94.2% homology with POX4 protein of C. tropicalis. One stretch of 36 aa shows no homology between the two proteins.

The nucleotide sequence of complementary DNA and the deduced amino acid sequence of peroxisomal catalase of the yeast Candida tropicalis pK233

We report the isolation and nucleotide (nt) sequence determination of cDNA encoding peroxisomal catalase (Cat) from the yeast Candida tropicalis pK233. The catalase cDNA (Cat) has a single open reading frame (ORF) of 1455 nt, encoding a protein of 484 amino acids (aa), not including the initiator methionine. The Mr of the protein is 54767. Codon use in the gene is not random, with 90.9% of the aa specified by 25 principal codons. The principal codons used in the expression of Cat in C. tropicalis are similar to those used in the expression of the fatty acyl-CoA oxidase gene of C. tropicalis and of highly expressed genes in Saccharomyces cerevisiae. Cat shows 48.0%, 49.7%, and 48.3% aa identity with human, bovine, and rat catalases, respectively, and 44.3% aa identity with catalase T of S. cerevisiae. The 3 aa of bovine liver catalase previously postulated to participate in catalysis and 79.5% of those aa in the immediate environment of hemin, the prosthetic group of catalase, are conserved in Cat of C. tropicalis.