The ARO4 gene of Candida albicans encodes a tyrosine-sensitive DAHP synthase: evolution, functional conservation and phenotype of Aro3p-, Aro4p-deficient mutants.
The enzyme 3-deoxy-D-arabinoheptulosonate-7-phosphate (DAHP) synthase catalyses the first step in aromatic amino acid biosynthesis in prokaryotes, plants and fungi. Cells of Saccharomyces cerevisiae contain two catalytically redundant DAHP synthases, encoded by the genes ARO3 and ARO4, whose activities are feedback-inhibited by phenylalanine and tyrosine, respectively. ARO3/4 gene transcription is controlled by GCN4. The authors previously cloned an ARO3 gene orthologue from Candida albicans and found that: (1) it can complement an aro3 aro4 double mutation in S. cerevisiae, an effect inhibited by excess phenylalanine, and (2) a homozygous aro3-deletion mutant of C. albicans is phenotypically Aro(+), suggesting the existence of another isozyme(s). They now report the identification and functional characterization of the C. albicans orthologue of S. cerevisiae Aro4p. The two Aro4p enzymes share 68% amino acid identity. Phylogenetic analysis places the fungal DAHP synthases in a cluster separate from prokaryotic orthologues and suggests that ARO3 and ARO4 arose from a single gene via a gene duplication event early in fungal evolution. C. albicans ARO4 mRNA is elevated upon amino acid starvation, consistent with the presence of three putative Gcn4p-responsive elements (GCREs) in the gene promoter sequence. C. albicans ARO4 complements an aro3 aro4 double mutation in S. cerevisiae, an effect inhibited by excess tyrosine. The authors engineered Deltaaro3/Deltaaro3 Deltaaro4/MET3p::ARO4 cells of C. albicans (with one wild-type copy of ARO4 placed under control of the repressible MET3 promoter) and found that they fail to grow in the absence of aromatic amino acids when ARO4 expression is repressed, and that this growth defect can be partially rescued by aromatic amino acids and certain aromatic amino acid pathway intermediates. It is concluded that, like S. cerevisiae, C. albicans contains two DAHP synthases required for the first step in the aromatic amino acid biosynthetic pathway.
Sousa
Silvino
S
Departments of Comparative Genomics1, Discovery Genetics2, Genomics Bioinformatics3, Microbial Bioinformatics and Microbial Genetics4, Glaxo SmithKline, King of Prussia, PA 19406, USA.
McLaughlin
Megan M
MM
Departments of Comparative Genomics1, Discovery Genetics2, Genomics Bioinformatics3, Microbial Bioinformatics and Microbial Genetics4, Glaxo SmithKline, King of Prussia, PA 19406, USA.
Pereira
Sarita A
SA
Departments of Comparative Genomics1, Discovery Genetics2, Genomics Bioinformatics3, Microbial Bioinformatics and Microbial Genetics4, Glaxo SmithKline, King of Prussia, PA 19406, USA.
VanHorn
Stephanie
S
Departments of Comparative Genomics1, Discovery Genetics2, Genomics Bioinformatics3, Microbial Bioinformatics and Microbial Genetics4, Glaxo SmithKline, King of Prussia, PA 19406, USA.
Knowlton
Robert
R
Departments of Comparative Genomics1, Discovery Genetics2, Genomics Bioinformatics3, Microbial Bioinformatics and Microbial Genetics4, Glaxo SmithKline, King of Prussia, PA 19406, USA.
Brown
James R
JR
Departments of Comparative Genomics1, Discovery Genetics2, Genomics Bioinformatics3, Microbial Bioinformatics and Microbial Genetics4, Glaxo SmithKline, King of Prussia, PA 19406, USA.
Nicholas
Richard O
RO
Departments of Comparative Genomics1, Discovery Genetics2, Genomics Bioinformatics3, Microbial Bioinformatics and Microbial Genetics4, Glaxo SmithKline, King of Prussia, PA 19406, USA.
Livi
George P
GP
Departments of Comparative Genomics1, Discovery Genetics2, Genomics Bioinformatics3, Microbial Bioinformatics and Microbial Genetics4, Glaxo SmithKline, King of Prussia, PA 19406, USA.
D010723:3-Deoxy-7-Phosphoheptulonate Synthase / Q000737:chemistry / Q000172:deficiency / Q000235:genetics*; D000595:Amino Acid Sequence; D024322:Amino Acids, Aromatic / Q000096:biosynthesis / Q000378:metabolism; D015139:Blotting, Southern; D002176:Candida albicans / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D025461:Feedback, Physiological; D017353:Gene Deletion; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D006720:Homozygote; D007527:Isoenzymes / Q000737:chemistry / Q000172:deficiency / Q000235:genetics; D008969:Molecular Sequence Data; D010641:Phenotype; D010802:Phylogeny; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D017386:Sequence Homology, Amino Acid
D024322:Amino Acids, Aromatic; D007527:Isoenzymes; D012331:RNA, Fungal; D012333:RNA, Messenger; D010723:3-Deoxy-7-Phosphoheptulonate Synthase