Glutamine:fructose-6-phosphate amidotransferase (glucosamine-6-phosphate synthase) catalyzes the first step of the hexosamine pathway required for the biosynthesis of cell wall precursors. The Candida albicans GFA1 gene was tinned by complementing a gfa1 mutation of Saccharomyces cerevisiae (previously known as gcn1-1; W. L. Whelan and C. E. Ballou, J. Bacteriol. 124:1545-1557, 1975). GFA1 encodes a predicted protein of 713 amino acids and is homologous to the corresponding gene from S. cerevisiae (72% identity at the nucleotide sequence level) as well as to the genes encoding glucosamine- 6-phosphate synthases in bacteria and vertebrates. In cell extracts, the C. albicans enzyme was 4-fold more sensitive than the S. cerevisiae enzyme to UDP-N-acetylglucosamine (an inhibitor of the mammalian enzyme) and 2.5-fold more sensitive to N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (a glutamine analog and specific inhibitor of glucosamine-6-phosphate synthase). Cell extracts from the S. cerevisiae gfa1 strain transformed with the C. albicans GFA1 gene exhibited sensitivities to glucosamine-6-phosphate synthase inhibitors that were similar to those shown by the C. albicans enzyme. Southern hybridization indicated that a single GFA1 locus exists in the C. albicans genome. Quantitative Northern (RNA) analysis showed that the expression of GFA1 in C. albicans is regulated during growth: maximum mRNA levels were detected during early log phase. GFA1 mRNA levels increased following induction of the yeast-to-hyphal-form transition, but this was a response to fresh medium rather than to the morphological change.
Bibliographical noteWe thank C. Ballou for S. cerevisiae XW270-2D, W. Tanner for plasmid YEpGW42, and M. Payton (Glaxo Institute for Molecular Biology, Geneva, Switzerland) for the C. albicans genomic library. We also thank Rolf Swoboda and Gwyneth Bertram for RNA samples used for Northern analysis. We are grateful to Bernie Hube, Mick
Tuite, Neil Gow, Barton Wicksteed, Rolf Swoboda, and Gwyneth Bertram for advice and discussion. This work was supported by the Science and Engineering Research
Council and The Wellcome Trust. S.M. was a Royal Society Postdoctoral Fellow. A.J.P.B. was awarded an Aberdeen University Research Fellowship.