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The ARG4 gene of Candida albicans
L L Hoyer1, B B Magee, E H Rikkerink
1Human Genome Center, Lawrence Berkeley Laboratory, University of California, Berkeley 94720.
Abstract:
The DNA sequence of a Candida albicans genomic fragment known to complement the arginine mutation designated arg57 in strain 1006 contains an ORF of 1404 nucleotides (nt) predicting a protein of 468 amino acids (aa). Database searches indicated that the deduced protein shares 75% identity and 85% similarity with the ARG4 protein of Saccharomyces cerevisiae. Analysis of the percent aa identity between C. albicans and S. cerevisiae sequences included in available databases suggested these values are within the range expected for biosynthetic enzymes from the two organisms which share similar function. Experiments to isolate C. albicans ARG4 by complementation in an arg4 strain of S. cerevisiae yielded a plasmid (pARG4-1) with a restriction map identical to that of the sequenced clone. From these data, we conclude that the gene previously designated ARG57 is in fact ARG4 encoding the enzyme argininosuccinate lyase (ASL). These results were unexpected, since ARG57 had been localized to chromosome 7, while a mutation causing an ASL deficiency had been linked to ade1, which is on chromosome R. Transformation of C. albicans strains with pARG4-1 indicated it complemented the arginine auxotrophy in strains TMSU221 and 1435, a derivative of 1006. Examination of commonly utilized C. albicans arginine auxotrophs by spheroplast fusion analysis indicated these strains comprise two complementation groups: one consisting of 1006 and TMSU221, which are arg4, and the other of A642, hOG318, hOG357, FC18-6 and WC-5-4, which possess an undefined defect in the arginine biosynthetic pathway which we designate arg100.
Insights
The Candida albicans ARG57 gene was identified as ARG4, encoding argininosuccinate lyase (ASL). This finding clarifies the arginine biosynthesis pathway and identifies a new complementation group, arg100.
Area of Science:
- Molecular Biology
- Mycology
- Biochemistry
Background:
- The arginine biosynthesis pathway in Candida albicans is crucial for fungal growth.
- Previous studies suggested a gene designated ARG57 complemented an arginine mutation, but its identity was unclear.
Purpose of the Study:
- To identify and characterize the gene responsible for complementing the arg57 mutation in Candida albicans.
- To resolve discrepancies in the genetic mapping of arginine auxotrophy in C. albicans.
Main Methods:
- DNA sequencing of a C. albicans genomic fragment.
- Database searches for protein homology.
- Complementation experiments in Saccharomyces cerevisiae.
- Plasmid isolation and characterization.
- Transformation of C. albicans strains.
- Spheroplast fusion analysis.
Main Results:
- A 1404-nucleotide open reading frame (ORF) was identified, predicting a 468-amino acid protein.
- The deduced protein showed high identity (75%) and similarity (85%) to Saccharomyces cerevisiae ARG4.
- The C. albicans gene complemented an arg4 mutation in S. cerevisiae, confirming its identity as ARG4.
- The gene complemented arginine auxotrophy in specific C. albicans strains (TMSU221 and 1435).
- Two complementation groups were identified among C. albicans arginine auxotrophs: arg4 and a newly defined arg100 group.
Conclusions:
- The gene previously designated ARG57 in Candida albicans is confirmed to be ARG4, encoding argininosuccinate lyase (ASL).
- This finding corrects previous genetic mapping data and clarifies the arginine biosynthetic pathway.
- A novel complementation group, arg100, representing an undefined defect in arginine biosynthesis, was identified.