Allelic frequencies and relationships for one dimorphic locus and three unlinked polymorphic loci have been determined for 114 unrelated isolates of Candida albicans, including 14 laboratory reference strains and 50 strains from each of two geographic regions. Although there was no indication of geographical partitioning, there were significant correlations for specific allelic pairs among loci and little evidence that any alleles were in HardyWeinberg equilibrium. This gives additional support for the concept that the primary mode of genetic inheritance in this species is clonal, with other intracellular genetic events playing a lesser role in the creation of genomic diversity. Through inference of this and other known attributes of closely related Candida species, such as sequence analysis of I S 1 and the ITS2 (internal transcribed spacer 2) region of the rDNA cistron, the deduced phylogeny suggests an evolutionarily recent origin for many frequently isolated strains. This finding will be of interest in the context of understanding pathogenicity and drug resistance in this human commensal yeast.

179The tripeptide L-methionyl-L-methionyl-L-[methyZ-14C]methionine was taken up into Candida albicans by a saturable system with a pH optimum of 3.5, a temperature optimum of 37 "C and an apparent K, of 3.

Carvone and perillaldehyde were shown to inhibit the transformation of Candida albicans to a filamentous form at concentrations far lower and more biologically relevant than the concentrations necessary to inhibit growth. This morphological transformation is associated with C. albicans pathogenicity; hence these naturally occurring monoterpenes are potential lead compounds in the development of therapeutic agents against C. albicans infection.

Abstract:The products of five structural genes and two regulatory genes of the qa gene cluster of Neurospora crassa control the metabolism of quinic acid (QA) as a carbon source. A detailed genetic network model of this metabolic process has been reported. This investigation is designed to expand the current model of the QA reaction network. The ensemble method of network identification was used to model RNA profiling data on the qa gene cluster. Through microarray and cluster analysis, genome-wide identification of RNA transcripts associated with quinic acid metabolism in N. crassa is described and suggests a connection to other metabolic circuits. More than 100 genes whose products include carbon metabolism, protein degradation and modification, amino acid metabolism and ribosome synthesis appear to be connected to quinic acid metabolism. The core of the qa gene cluster network is validated with respect to RNA profiling data obtained from microarrays.Keywords: genetic networks; quinic acid; qa gene cluster; genome; microarray Background:Advances in systems biology and the relative ease of manipulating eukaryotic microorganisms such as fungi have made it possible to elucidate a complex trait such as how a cell metabolizes a carbon source. The genetics of the metabolism of the carbon compound quinic acid in Neurospora crassa is one of the early paradigms for eukaryotic gene regulation with the support of over four decades of genetics and biochemistry. [2] The network involves 54 reactions and 38 macromolecules and small molecules and is based on a kinetics framework [3] and experimental data generated over a span of more than three decades. [4] In the diagram, circles, boxes and arrows depict, reactions, molecular species, and the flow of reactants and products for the reaction proceeding "forward". Reactions without outgoing arrows (lollipops), indicate decay reactions. Reactants include the seven genes of the qa gene cluster (qa-x, qa-2, qa-3, qa-4, qa-y, qa-1S, qa-1F) [1] with superscripts "0" or "1" indicating the presence or absence, respectively, of a bound transcriptional activator, encoded by the qa-1F gene. These genes are transcribed into RNA molecules (superscript r), which in turn are translated into protein products (in capital letters). Four out of seven proteins have been demonstrated by experimental means to participate in a known biochemical pathway at the bottom of the diagram. There are at least two cellular states for quinic acid, extracellular (depicted as QA

An ensemble of genetic networks that describe how the model fungal system, Neurospora crassa, utilizes quinic acid (QA) as a sole carbon source has been identified previously. A genetic network for QA metabolism involves the genes, qa-1F and qa-1S, that encode a transcriptional activator and repressor, respectively and structural genes, qa-2, qa-3, qa-4, qa-x, and qa-y. By a series of 4 separate and independent, model-guided, microarray experiments a total of 50 genes are identified as QA-responsive and hypothesized to be under QA-1F control and/or the control of a second QA-responsive transcription factor (NCU03643) both in the fungal binuclear Zn(II)2Cys6 cluster family. QA-1F regulation is not sufficient to explain the quantitative variation in expression profiles of the 50 QA-responsive genes. QA-responsive genes include genes with products in 8 mutually connected metabolic pathways with 7 of them one step removed from the tricarboxylic (TCA) Cycle and with 7 of them one step removed from glycolysis: (1) starch and sucrose metabolism; (2) glycolysis/glucanogenesis; (3) TCA Cycle; (4) butanoate metabolism; (5) pyruvate metabolism; (6) aromatic amino acid and QA metabolism; (7) valine, leucine, and isoleucine degradation; and (8) transport of sugars and amino acids. Gene products both in aromatic amino acid and QA metabolism and transport show an immediate response to shift to QA, while genes with products in the remaining 7 metabolic modules generally show a delayed response to shift to QA. The additional QA-responsive cutinase transcription factor-1β (NCU03643) is found to have a delayed response to shift to QA. The series of microarray experiments are used to expand the previously identified genetic network describing the qa gene cluster to include all 50 QA-responsive genes including the second transcription factor (NCU03643). These studies illustrate new methodologies from systems biology to guide model-driven discoveries about a core metabolic network involving carbon and amino acid metabolism in N. crassa.