Isolation of a gene encoding a putative polyamine transporter from Candida albicans, GPT1

A gene encoding a transport protein from the pathogenic yeast, Candida albicans, has been isolated during a complementation experiment utilizing an ornithine decarboxylase-negative (spe1 Delta) strain of Saccharomyces cerevisiae. This gene restores gamma-aminobutyric acid (GABA) transport to a GABA transport-negative mutant of S. cerevisiae and encodes a protein which putatively allows transport of one or more of the polyamines. We have assigned the name GPT1 (GABA/polyamine transporter) to this gene.     

Isolation and characterization of the Candida albicans SEC4 Gene

The SEC4 gene product is a major component of the protein secretion machinery. More specifically, it is believed to play a pivotal role in targeting and fusion of secretory vesicles to the plasma membrane. Its recently described implication with the Saccharomyces cerevisiae Rho3p, which is required for directing growing points during bud formation, has prompted us to investigate the role and function of Sec4p in the morphological changes of the yeast pathogen Candida albicans. We have therefore cloned the C. albicans SEC4 gene. It encodes a 210 amino acids long protein sharing up to 75% homology to the S. cerevisiae homolog, when conserved changes are allowed. Its RNA is constitutively expressed in C. albicans grown under various physiological conditions. We also show that it can functionally complement a S. cerevisiae sec4 thermosensitive mutant. The sequence of the C. albicans SEC4 gene has been deposited in GenBank under Accession Number AF017183. © 1998 John Wiley & Sons, Ltd.     

Characterization of Candida albicans orthologue of the Saccharomyces cerevisiae signal-peptidase-subunit encoding gene SPC3

The Candida albicans orthologue of the SPC3 gene, which encodes one of the subunits essential for the activity of the signal peptidase complex in Saccharomyces cerevisiae, was isolated by complementation of a thermosensitive mutation in the S. cerevisiae SEC61 gene. The cloned gene (CaSPC3) encodes a putative protein of 192 amino acids that contains one potential membrane-spanning region and shares significant homology with the corresponding products from mammalian (Spc22/23p) and yeast (Spc3p) cells. CaSPC3 is essential for cell viability, since a hemizygous strain containing a single copy of CaSPC3 under control of the methionine-repressible MET3 promoter did not grow in the presence of methionine and cysteine. The cloned gene could rescue the phenotype associated with a spc3 mutation in S. cerevisiae, indicating that it is the true C. albicans orthologue of SPC3. However, in contrast with results previously described for its S. cerevisiae orthologue, CaSPC3 was not able to complement the thermosensitive growth associated with a mutation in the SEC11 gene. The heterologous complementation of the sec61 mutant suggests that Spc3p could play a role in the interaction that it is known to occur between the translocon (Sec61 complex) and the signal peptidase complex, at the endoplasmic reticulum membrane.     

Isolation and sequence of the gene encoding ornithine decarboxylase,SPE1, from Candida albicans by complementation of a spe1Δ ctrain of Saccharomyces cerevisiae

The gene encoding ornithine decarboxylase, SPE1, from the pathogenic yeast Candida albicans has been isolated by complementation of an ornithine decarboxylase-negative (spe1Δ) strain of Saccharomyces cerevisiae. Four transformants, three of which contain plasmids with the SPE1 gene, were isolated by selection on polyamine-free medium. The C. albicans ornithine decarboxylase (ODC) showed high homology with other eukaryotic ODCs at both the amino acid and nucleic acid levels. The GenBank accession number for this gene is U85005. © 1997 John Wiley & Sons, Ltd.     

A Candida albicans gene encoding a DNA ligase

A DNA ligase-encoding gene (Ca CDC9) was cloned from Candida albicans by complementation of an ime-1 mutation in Saccharomyces cerevisiae. In this system, IME1 function was assayed using a S. cerevisiae strain with a ime2-promoter-lacZ gene fusion such that following transformation with a C. albicans genomic library, the presence of positive clones was indicated upon the addition of X-gal to sporulation media. Transforming fragments were subcloned in pGEM7 and sequenced. Sequence homology with several ATP-dependent DNA ligases from viruses, fission yeast, human, baker yeast and bacteria was observed. The sequence has been deposited in the EMBL data bank under the Accession Number X95001.     

The Candida albicans 14-3-3 gene, BMH1, is essential for growth.

The 14-3-3 proteins are a family of conserved small acidic proteins that have been implicated in playing major roles in a wide variety of signalling cascades. In Saccharomyces cerevisiae, the 14-3-3 genes (BMH1 and BMH2) are essential for normal pseudohyphal induction and normal bud cell development. The Bmh proteins function in the cAMP-dependent RAS/MAPK and rapamycin-sensitive signalling cascades. Deletion of only one BMH gene demonstrates no phenotypic differences under normal growth conditions. Strains deleted of both BMH1 and BMH2 are either non-viable or demonstrate sensitivity to environmental stresses. In Schizosaccharomyces pombe, the BMH homologues (RAD24 and RAD25) are essential for cell cycle control after DNA damage and deletion of both genes renders the cell inviable. The 14-3-3 gene in Candida albicans (BMH1) was identified using a novel adherence assay and differential display RT-PCR. Unlike other yeasts, C. albicans has only one 14-3-3 gene (BMH1). It was not possible to construct double knockouts by routine methods. These results suggested that the C. albicans BMH1 gene is essential. The essentiality of C. albicans BMH1 was confirmed by a PCR disruption technique. The C. albicans bmh1 Delta/BMH1 heterozygotes exhibit growth and morphogenetic defects. Therefore, the BMH1 gene in C. albicans (Accession No. AF038154) is an excellent candidate to improve our understanding of the coordinate regulation of cell cycle and morphogenesis.     

Functional analysis of the Candida albicans ALS1 gene product

ALS1 encodes a cell surface protein that mediates adherence of Candida albicans to endothelial cells. The predicted Als1p has an N-terminal region, which contains a signal peptide; a middle region, which contains 20 36-amino acid tandem repeats; and a C-terminal region, which contains a glycosylphosphotidylinositol-anchorage sequence. We used site-directed mutagenesis to delineate the regions in Als1p required for endothelial cell adherence and cell surface expression of the protein. Mutant alleles of ALS1 containing either deletions or insertions were expressed in the normally non-adherent Saccharomyces cerevisiae. These transformants were analysed for endothelial cell adherence and cell surface expression of Als1p. We found that mutations centred around amino acid 285 in the N-terminus completely abolished adherence, but had no effect on cell surface expression of Als1p. Deletion of 15 of the tandem repeats reduced adherence by 50%, whereas deletion of all abolished adherence completely, even though cell surface expression of the N-terminus of Als1p was maintained. Insertions into the C-terminus at amino acids 413 and 254 upstream of the stop codon resulted in a modest loss of adherence, while cell surface expression of Als1p was maintained. An insertion at amino acid 249 in the C-terminus caused complete loss of both adherence and cell surface expression, even though the glycosylphosphotidylinositol-anchorage sequence remained intact. These data suggest a model of Als1p in which the endothelial cell binding region is localized within its N-terminus, the tandem repeats are essential for the proper presentation of the binding site, and the C-terminus is required for localizing Als1p to the cell surface.     

Stop codon decoding in Candida albicans: from non-standard back to standard

The human pathogen Candida albicans translates the standard leucine-CUG codon as serine. This genetic code change is mediated by a novel ser-tRNA(CAG), which induces aberrant mRNA decoding in vitro, resulting in retardation of the electrophoretic mobility of the polypeptides synthesized in its presence. These non-standard decoding events have been attributed to readthrough of the UAG and UGA stop codons encoded by the Brome Mosaic Virus RNA 4, which codes for the virion coat protein, and the rabbit globin mRNAs, respectively. In order to fully elucidate the behaviour of the C. albicans ser-tRNA(CAG) towards stop codons, we have used other cell-free translation systems and reporter genes. However, the reporter systems used encode several CUG codons, making it impossible to distinguish whether the slow migration of the polypeptides is caused by the replacement of leucines by serines at the CUG codons, readthrough, or a combination of both. Therefore, we have constructed new reporter systems lacking CUG codons and have used them to demonstrate that aberrant mRNA decoding in vitro is not a result from stop codon readthrough or any other non-standard translational event. Our data show that a single leucine to serine replacement at only one of the four CUG codons encoded by the BMV RNA-4 gene is responsible for the aberrant migration of the BMV coat protein on SDS-PAGE, suggesting that this amino acid substitution (ser for leu) significantly alters the structure of the virion coat protein. The data therefore show that the only aberrant event mediated by the ser-tRNA(CAG) is decoding of the leu-CUG codon as serine.     

Isolation and Characterization of the Candida albicans PFY1 Gene for Profilin

We have isolated the Candida albicans gene for profilin, PFY1. Degenerate oligonucleotide primers based on regions of high homology were utilized to obtain a polymerase chain reaction-amplified copy of the gene. This was then used as a probe to isolate the gene from a C. albicans genomic library. Our studies indicate that the full-length gene is unstable in Escherichia coli. Several clones were sequenced, and the predicted amino acid sequence demonstrated homology with profilin proteins from other organisms, most notably Saccharomyces cerevisiae. Northern analysis revealed that the gene is expressed in C. albicans. Attempts to express the gene in S. cerevisiae cells were unsuccessful until the C. albicans promoter was replaced with an S. cerevisiae promoter. Functional complementation of the gene was demonstrated in S. cerevisiae profilin-requiring cells. Antibodies raised to isolated C. albicans profilin protein recognized a protein of the predicted molecular weight when the gene was expressed in S. cerevisiae cells. The sequence of the C. albicans PFY1 gene has been deposited in the Genome Sequence database under Accession Number L3783. © 1997 John Wiley & Sons, Ltd.     

The SPL1 tRNA splicing gene of Candida maltosa and Candida albicans

The tRNA splicing gene SPL1-1 has been cloned and sequenced in Saccharomyces cerevisiae (Kolman and Soll, 1993). Sequence adjacent to the LEU2 gene in Candida maltosa showed some homology to the SPL1-1 gene of S. cerevisiae. This work describes the sequencing of the SPL1 tRNA splicing genes from C. maltosa and C. albicans and the analysis of these genes. Comparison of these sequences and the relationship observed between the LEU2 and SPL1 genes in these yeasts suggests that there may be some synteny amongst various species of yeasts. The coding region of the C. maltosa SPL1 region described in this work differs from previously described partial sequences in that it is a complete uninterrupted open reading frame. Two strains of C. maltosa were each shown to contain different alleles, one uninterrupted open reading frame and one disrupted open reading frame. The sequences have been deposited in the GenBank/EMBL data libraries under Accession Numbers X72940, AF000115, AF000116, AF000117, AF000118, AF000119 and AF000120. © 1998 John Wiley & Sons, Ltd.     

Yeast sequencing reports. CAN1, a gene encoding a permease for basic amino acids in Candida albicans

The first gene coding for an amino-acid permease of Candida albicans was sequenced. The DNA fragment complementing the lysine-permease deficiency was 3385 bp long. An open reading frame of 1713 nucleotides was found encoding a protein of 571 amino acids, with a calculated molecular weight of 63 343. Analysis of the deduced primary structure revealed ten membrane spanning regions and three potential N-glycosylation sites. The protein sequence is strongly homologous to both permeases for basic amino acids (Can1 and Lyp1) of Saccharomyces cerevisiae. C-terminal part of another ORF (105 aa), highly homologous to the gene HAL2 of S. cerevisiae, was found 133 bp downstream, and in tail-to-tail orientation to the permease gene. The sequence data will appear in the EMBL/GenBank/DDBJ Nucleotide Sequence Data Libraries under the accession number X76689.