Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Loss of Function Mutation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed2005

A rapid PCR method for genotyping the Large(myd) mouse, a model of glycosylation-deficient congenital muscular dystrophy.

The myodystrophy (Large(myd)) mouse has a spontaneous loss of function mutation in a putative glycosyltransferase gene (Large). Mutations in the human gene (LARGE) have been described in congenital muscular dystrophy type 1D (MDC1D). Mutations in four other genes that encode known or putative glycosylation enzymes (POMT1, POMGnT1, fukutin and FKRP) are also associated with muscular dystrophy. In all these diseases hypoglycosylation of alpha-dystroglycan, and consequent loss of ligand binding, is a common pathomechanism. Currently, the Large(myd) mouse is the principal animal model for studying the underlying molecular mechanisms of this group of disorders. Over-expression of LARGE in cells from patients with mutations in POMT1 or POMGnT1 results in hyperglycosylation of alpha-dystroglycan and restoration of laminin binding. Thus, LARGE is a potential therapeutic target. Here, we define the intronic deletion breakpoints of the Large(myd) mutation and describe a simple, PCR-based diagnostic assay, facilitating the study of this important animal model.

Animals↗
PubMed1999

Lethal paralysis of Caenorhabditis elegans by Pseudomonas aeruginosa.

Identification of host factors that interact with pathogens is crucial to an understanding of infectious disease, but direct screening for host mutations to aid in this task is not feasible in mammals. The nematode Caenorhabditis elegans is a genetically tractable alternative for investigating the pathogenic bacterium Pseudomonas aeruginosa. A P. aeruginosa toxin, produced at high cell density under control of the quorum-sensing regulators LasR and RhlR, rapidly and lethally paralyzes C. elegans. Loss-of-function mutations in C. elegans egl-9, a gene required for normal egg laying, confer strong resistance to the paralysis. Thus, activation of EGL-9 or of a pathway that includes it may lead to the paralysis. The molecular identity of egl-9 was determined by transformation rescue and DNA sequencing. A mammalian homologue of EGL-9 is expressed in tissues in which exposure to P. aeruginosa could have clinical effects.

Amino Acid Sequence↗
PubMed1998

The human Rh50 glycoprotein gene. Structural organization and associated splicing defect resulting in Rh(null) disease.

The Rh (Rhesus) protein family comprises Rh50 glycoprotein and Rh30 polypeptides, which form a complex essential for Rh antigen expression and erythrocyte membrane integrity. This article describes the structural organization of Rh50 gene and identification of its associated splicing defect causing Rhnull disease. The Rh50 gene, which maps at chromosome 6p11-21.1, has an exon/intron structure nearly identical to Rh30 genes, which map at 1p34-36. Of the 10 exons assigned, conservation of size and sequence is confined mainly to the region from exons 2 to 9, suggesting that RH50 and RH30 were formed as two separate genetic loci from a common ancestor via a transchromosomal insertion event. The available information on the structure of RH50 facilitated search for candidate mutations underlying the Rh deficiency syndrome, an autosomal recessive disorder characterized by mild to moderate chronic hemolytic anemia and spherostomatocytosis. In one patient with the Rhnull disease of regulator type, a shortened Rh50 transcript lacking the sequence of exon 7 was detected, while no abnormality was found in transcripts encoding Rh30 polypeptides and Rh-related CD47 glycoprotein. Amplification and sequencing of the genomic region spanning exon 7 revealed a G-->A transition in the invariant GT motif of the donor splice site in both Rh50 alleles. This splicing mutation caused not only a total skipping of exon 7 but also a frameshift and premature chain termination. Thus, the deduced translation product contained 351 instead of 409 amino acids, with an entirely different C-terminal sequence following Thr315. These results identify the donor splicing defect, for the first time, as a loss-of-function mutation at the RH50 locus and pinpoint the importance of the C-terminal region of Rh50 in Rh complex formation via protein-protein interactions.

Amino Acid Sequence↗
PubMed2000

The nuclease activity of the yeast DNA2 protein, which is related to the RecB-like nucleases, is essential in vivo.

Saccharomyces cerevisiae Dna2 protein is required for DNA replication and repair and is associated with multiple biochemical activities: DNA-dependent ATPase, DNA helicase, and DNA nuclease. To investigate which of these activities is important for the cellular functions of Dna2, we have identified separation of function mutations that selectively inactivate the helicase or nuclease. We describe the effect of six such mutations on ATPase, helicase, and nuclease after purification of the mutant proteins from yeast or baculovirus-infected insect cells. A mutation in the Walker A box in the C-terminal third of the protein affects helicase and ATPase but not nuclease; a mutation in the N-terminal domain (amino acid 504) affects ATPase, helicase, and nuclease. Two mutations in the N-terminal domain abolish nuclease but do not reduce helicase activity (amino acids 657 and 675) and identify the putative nuclease active site. Two mutations immediately adjacent to the proposed nuclease active site (amino acids 640 and 693) impair nuclease activity in the absence of ATP but completely abolish nuclease activity in the presence of ATP. These results suggest that, although the Dna2 helicase and nuclease activities can be independently affected by some mutations, the two activities appear to interact, and the nuclease activity is regulated in a complex manner by ATP. Physiological analysis shows that both ATPase and nuclease are important for the essential function of DNA2 in DNA replication and for its role in double-strand break repair. Four of the nuclease mutants are not only loss of function mutations but also exhibit a dominant negative phenotype.

Amino Acid Sequence↗
PubMed2006

SRY-negative 46,XX male with normal genitals, complete masculinization and infertility.

XX maleness is a rare syndrome with a frequency of 1 in 20,000-25,000 males. XX males exist in different clinical categories with ambiguous genitalia or partially to fully mature male genitalia, in combination with complete or incomplete masculinization. In this study, we report a case of SRY-negative XX male with complete masculinization but infertility. The patient had fully mature male genitalia with descended but small testes and no signs of undervirilization. PCR analysis for SRY, ZFY, Amelogenin, AZFa, AZFb, AZFc genes, a pair of primers from heterochromatic region and six Y-STRs showed the absence of any Y-chromosome-derived material. Absence of SRY gene was confirmed by three independent PCRs for each of two sets of primers covering an increasing length of the gene. Sequence analysis of the coding regions of SOX9 and DAX1 genes did not reveal any mutation. Real-time PCR assay revealed normal copy number for SOX9 gene. Microsatellite analysis showed no evidence of 17q (SOX9 gene) or 22q duplication. Genotyping with X-STRs ruled out the possibility of any deletion on X chromosome. Development of the male phenotype in the absence of SRY probably resulted from the loss of function mutation in some unknown sex-determining gene, which normally inhibits the male pathway, or from a gain of function mutation in a gene downstream to SRY in male pathway.

Adult↗
PubMed2025

Developing a disease-specific accessible transcriptional signature as a biomarker for ataxia with oculomotor apraxia type 2.

BACKGROUND: Genetic ataxias are clinically heterogenous neurodegenerative conditions often involving rare or private mutations and it is often difficult to assign pathogenicity to rare gene variants solely based on DNA sequencing. An effective functional assay from an easy-to-obtain biospecimen would aid this assessment and be of high clinical value. SETX encodes a ubiquitous DNA/RNA helicase crucial for resolving R-loops and maintaining genome stability. Loss-of-function mutations cause a recessive disorder, Ataxia with Oculomotor Apraxia Type 2 (AOA2). METHODS: Here we utilize Weighted Gene Co-expression Network Analysis (WGCNA) from patient blood to construct an AOA2-specific transcriptomic signature as a biomarker to evaluate SETX variants in patients clinically suspected of having AOA2. RESULTS: WGCNA from peripheral blood RNA of 11 AOA2 patients from 7 families initially identified a single gene module that was modestly effective in distinguishing individuals with AOA2 from controls (sensitivity 73%, specificity 97%) and was able to robustly differentiate AOA2 patients from those with genetically distinct, yet phenotypically similar, neurological disorders (sensitivity 100%, specificity 100%). An independent derivation of the transcriptional biomarker identified a dual module model that was able to better distinguish individuals with AOA2 from controls (sensitivity 100%, specificity 97%). As validation, we examined a second cohort of 21 patients from 13 families and demonstrate that this dual module transcriptional biomarker could discriminate patients clinically suspected of AOA2 from controls (57%, 95%CI: 34%-78%). Overall, the transcriptional biomarker was able to separate AOA2 subjects (n = 32) from controls (n = 35) with 72% sensitivity and 97% specificity. Notably, this transcriptomic biomarker enabled verification of the first pathogenic SETX mutation found in a non-canonical transcript, expanding the spectrum of mutations that contribute to AOA2. CONCLUSIONS: Our study identified a transcriptional biomarker that was able to differentiate AOA2 from controls and from other related neurological disorders, consequently expanding the spectrum of known pathogenic mutations. This proof-of-concept study illustrates that transcriptional biomarkers may be used to validate variants of uncertain significance in known genetic diseases.

Humans↗
PubMed2006

GLABROUS INFLORESCENCE STEMS modulates the regulation by gibberellins of epidermal differentiation and shoot maturation in Arabidopsis.

As a plant shoot matures, it transitions through a series of growth phases in which successive aerial organs undergo distinct developmental changes. This process of phase change is known to be influenced by gibberellins (GAs). We report the identification of a putative transcription factor, GLABROUS INFLORESCENCE STEMS (GIS), which regulates aspects of shoot maturation in Arabidopsis thaliana. GIS loss-of-function mutations affect the epidermal differentiation of inflorescence organs, causing a premature decrease in trichome production on successive leaves, stem internodes, and branches. Overexpression has the opposite effect on trichome initiation and causes other heterochronic phenotypes, affecting flowering and juvenile-adult leaf transition and inducing the formation of rosette leaves on inflorescence stems. Genetic and gene expression analyses suggest that GIS acts in a GA-responsive pathway upstream of the trichome initiation regulator GLABROUS1 (GL1) and downstream of the GA signaling repressor SPINDLY (SPY). GIS mediates the induction of GL1 expression by GA in inflorescence organs and is antagonized in its action by the DELLA repressor GAI. The implication of GIS in the broader regulation of phase change is further suggested by the delay in flowering caused by GIS loss of function in the spy background. The discovery of GIS reveals a novel mechanism in the control of shoot maturation, through which GAs regulate cellular differentiation in plants.

Amino Acid Sequence↗
PubMed1998

Novel compound heterozygous laminina2-chain gene (LAMA2) mutations in congenital muscular dystrophy. Mutations in brief no. 159. Online.

The laminina2-chain gene (LAMA2) encodes a basal lamina protein, laminina2, known to be deficient in one form of congenital muscular dystrophy (CMD). In a laminina2 deficient-CMD patient, we screened the entire LAMA2 cDNA (953bp) by reverse transcriptase polymerase chain reaction combined with single strand conformational polymorphism analysis. Direct sequencing of aberrant conformers in this patient revealed two loss-of-function mutations, consistent with autosomal recessive inheritance. The patient had two novel heterozygous mutations: 1) an exon 4 nonsense mutation caused by a G-->A substitution at cDNA position 547, changing the TGG codon for tryptophan into a TGA stop codon (W166X) in the N-terminus domain VI;ii) an exon 54 frameshift mutation due to a deletion of nucleotide 'C' at cDNA position 7707 (S2553Y), resulting in a premature stop codon (V2587X) in exon 55 in the globular G domain of laminina2 at the C-terminus. These mutations cause a disruption of the open reading frame of LAMA2. The absence of laminina2 observed in the patient's muscle biopsy could result from diminished levels of the LAMA2 transcript. Alternatively, the mutations might lead to translation of a truncated laminina2. By either mechanism the phenotype of congenital muscular dystrophy is believed to be the result of disruption of linkage between the extracellular matrix and the dystrophin glycoprotein complex.

DNA Mutational Analysis↗
PubMed2004

Mutations within the MGC4607 gene cause cerebral cavernous malformations.

Cerebral cavernous malformations (CCM) are hamartomatous vascular malformations characterized by abnormally enlarged capillary cavities without intervening brain parenchyma. They cause seizures and focal neurological deficits due to cerebral hemorrhages. CCM loci have already been assigned to chromosomes 7q (CCM1), 7p (CCM2), and 3q (CCM3) and have been identified in 40%, 20%, and 40%, respectively, of families with CCM. Loss-of-function mutations have been identified in CCM1/KRIT1, the sole CCM gene identified to date. We report here the identification of MGC4607 as the CCM2 gene. We first reduced the size of the CCM2 interval from 22 cM to 7.5 cM by genetic linkage analysis. We then hypothesized that large deletions might be involved in the disorder, as already reported in other hamartomatous conditions, such as tuberous sclerosis or neurofibromatosis. We performed a high-density microsatellite genotyping of this 7.5-cM interval to search for putative null alleles in 30 unrelated families, and we identified, in 2 unrelated families, null alleles that were the result of deletions within a 350-kb interval flanked by markers D7S478 and D7S621. Additional microsatellite and single-nucleotide polymorphism genotyping showed that these two distinct deletions overlapped and that both of the two deleted the first exon of MGC4607, a known gene of unknown function. In both families, one of the two MGC4607 transcripts was not detected. We then identified eight additional point mutations within MGC4607 in eight of the remaining families. One of them led to the alteration of the initiation codon and five of them to a premature termination codon, including one nonsense, one frameshift, and three splice-site mutations. All these mutations cosegregated with the disease in the families and were not observed in 192 control chromosomes. MGC4607 is so far unrelated to any known gene family. Its implication in CCMs strongly suggests that it is a new player in vascular morphogenesis.

Female↗
PubMed2005

The fork head transcription factor FKTF-1b from Strongyloides stercoralis restores DAF-16 developmental function to mutant Caenorhabditis elegans.

The purpose of this study was to determine whether Strongyloides stercoralis FKTF-1, a transcription factor of the FOXO/FKH family and the likely output of insulin/IGF signal transduction in that parasite, has the same or similar developmental regulatory capabilities as DAF-16, its structural ortholog in Caenorhabditis elegans. To this end, both splice variants of the fktf-1 message were expressed under the control of the daf-16alpha promoter in C. elegans carrying loss of function mutations in both daf-2 (the insulin/IGF receptor kinase) and daf-16. Under well-fed culture conditions the majority (91%) of untransformed daf-2; daf-16 double mutants developed via the continuous reproductive cycle, whereas under the same conditions 100% of daf-2 single mutants formed dauers. Transgenic daf-2; daf-16 individuals expressing fktf-1b showed a reversal of the double mutant phenotype with 75% of the population forming dauers under well-fed conditions. This phenotype was even more pronounced than that of daf-2; daf-16 mutants transformed with a homologous rescuing construct, daf-16alpha::daf-16a (56% dauers under well fed conditions), indicating that S. stercoralis fktf-1b can almost fully rescue loss-of-function mutants in C. elegans daf-16. By contrast, daf-2; daf-16 mutants expressing S. stercoralis fktf-1a, encoding the second splice variant of FKTF-1, showed a predominantly continuous pattern of development identical to that of the parental double mutant stock. This indicates that, unlike FKTF-1b, the S. stercoralis transcription factor FKTF-1a cannot trigger the shift to dauer-specific gene expression in C. elegans.

Animals↗
PubMed2005

Role of ferritin and ferroportin genes in unexplained hyperferritinaemia.

A large body of evidence indicates that the level of serum ferritin parallels the concentration of storage iron within the body, regardless of the cell type in which it is stored. Elevated serum ferritin levels, in the absence of inflammation and liver disease, are currently taken to indicate increased iron stores and require further investigation to determine the site of iron overload. Until recently, the only genetic disorder with elevated serum ferritin levels known in Western countries was hereditary HLA-related HFE-related genetic haemochromatosis in Caucasians (HFE, OMIM 235200), and a high serum ferritin in apparently healthy persons was considered suggestive of this disease. In the last few years, at least two novel genetic disorders of iron metabolism presenting as unexplained hyperferritinaemia have been recognized. The first one is hereditary hyperferritinaemia/cataract syndrome (HHCS, OMIM 600886). HHCS arises from various point mutations or deletions within a protein binding sequence in the 5'-UTR of the L-ferritin mRNA that results in increased efficiency of L-ferritin translation. The second one is haemochromatosis type 4, or HFE4 (OMIM 606069), or ferroportin disease. In this latter condition, reticuloendothelial iron overload and hyperferritinaemia are caused by loss-of-function mutations in the SLC11A3 gene that mainly impair macrophage iron recycling. These genetic disorders should be taken into account in the differential diagnosis of unexplained hyperferritinaemia.

Anemia↗
PubMed2006

Gene trapping in embryonic stem cells.

Gene trapping in embryonic stem cells (ESCs) generates random, sequence-tagged insertional mutations, which can often report the gene expression pattern of the mutated gene. This mutagenesis strategy has often been coupled to expression or function-based assays in gene discovery screens. The availability of the mouse genome sequence has shifted gene trapping from a gene discovery platform to a high-throughput mutagenesis platform. At present, a concerted worldwide effort is underway to develop a library of loss-of-function mutations in all mouse genes. The International Gene Trap Consortium (IGTC) is leading the way by making a first pass of the genome by random mutagenesis before a high-throughput gene targeting program takes over. In this chapter, we provide a methods guidebook to exploring and using the IGTC resource, explain the different kinds of vectors and insertions that reside in the different libraries, and provide advice and methods for investigators to design novel expression-based "cottage industry" screens.

Animals↗
PubMed2000

C-cell hyperplasia, pheochromocytoma and sympathoadrenal malformation in a mouse model of multiple endocrine neoplasia type 2B.

Dominantly inherited multiple endocrine neoplasia type 2B (MEN2B) is characterized by tumors of the thyroid C-cells and adrenal chromaffin cells, together with ganglioneuromas of the gastrointestinal tract and other developmental abnormalities. Most cases are caused by substitution of threonine for Met918 in the RET receptor tyrosine kinase, which is believed to convert the RET gene to an oncogene by altering the enzyme's substrate specificity. We report the production of a mouse model of MEN2B by introduction of the corresponding mutation into the ret gene. Mutant mice displayed C-cell hyperplasia and chromaffin cell hyperplasia progressing to pheochromocytoma. Homozygotes did not develop gastrointestinal ganglioneuromas, but displayed ganglioneuromas of the adrenal medulla, enlargement of the associated sympathetic ganglia and a male reproductive defect. Surprisingly, homozygotes did not display any developmental defects attributable to a loss-of-function mutation. Thus, while our results support the conclusion that the Met918Thr substitution is responsible for MEN2B, they suggest that the substrate specificity of the RET kinase does not interfere with its normal role in the development of the kidneys and enteric nervous system.

Adrenal Gland Neoplasms↗
PubMed1995

Interacting genes required for pharyngeal excitation by motor neuron MC in Caenorhabditis elegans.

We studied the control of pharyngeal excitation in Caenorhabditis elegans. By laser ablating subsets of the pharyngeal nervous system, we found that the MC neuron type is necessary and probably sufficient for rapid pharyngeal pumping. Electropharyngeograms showed that MC transmits excitatory postsynaptic potentials, suggesting that MC acts as a neurogenic pacemaker for pharyngeal pumping. Mutations in genes required for acetylcholine (ACh) release and an antagonist of the nicotinic ACh receptor (nAChR) reduced pumping rates, suggesting that a nAChR is required for MC transmission. To identify genes required for MC neurotransmission, we screened for mutations that cause slow pumping but no other defects. Mutations in two genes, eat-2 and eat-18, eliminated MC neurotransmission. A gain-of-function eat-18 mutation, ad820sd, and a putative loss-of-function eat-18 mutation, ad1110, both reduced the excitation of pharyngeal muscle in response to the nAChR agonists nicotine and carbachol, suggesting that eat-18 is required for the function of a pharyngeal nAChR. Fourteen recessive mutations in eat-2 fell into five complementation classes. We found allele-specific genetic interactions between eat-2 and eat-18 that correlated with complementation classes of eat-2. We propose that eat-18 and eat-2 function in a multisubunit protein complex involved in the function of a pharyngeal nAChR.

Animals↗
PubMed2002

Neuropathological changes in a mouse model of progressive myoclonus epilepsy: cystatin B deficiency and Unverricht-Lundborg disease.

Progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1) is a recessively inherited neurodegenerative disease caused by loss-of-function mutations in the gene encoding cystatin B, a cysteine protease inhibitor. Mice with disruptions in this gene display myoclonic seizures, progressive ataxia, and cerebellar pathology closely paralleling EPMI in humans. To provide further insight into our understanding of EPM1, we report pathological findings in brains from cystatin B-deficient mice. In addition to confirming the loss of cerebellar granular cell neurons by apoptosis, we identified additional neuronal apoptosis in young mutant mice (3-4 months old) within the hippocampal formation and entorhinal cortex. In older mutant mice (16-18 months old), there was also gliosis most marked in the presubiculum and parasubiculum of the hippocampal formation, as well as the entorhinal cortex, neocortex, and striatum. Furthermore, widespread white matter gliosis was also noted, which may be a secondary phenomenon. Within the cerebral cortex, cellular atrophy was a prominent finding in the superficial neurons of the prosubiculum. Finally, we show that mutant mice in either a "seizure-prone" or "seizure-resistant" genetic background display similar neuropathological changes. These findings indicate that neuronal atrophy is an important consequence of cystatin-B deficiency independent of seizure events, suggesting a physiological role for this protein in the maintenance of normal neuronal structure.

Animals↗
PubMed2005

The small GTPase Rac plays multiple roles in epithelial sheet fusion--dynamic studies of Drosophila dorsal closure.

The coordinated migration and fusion of epithelial sheets is a crucial morphogenetic tool used on numerous occasions during the normal development of an embryo and re-activated as part of the wound healing response. Drosophila dorsal closure, whereby a hole in the embryonic epithelium is zipped closed late in embryogenesis, serves as an excellent, genetically tractable model for epithelial migration. Using live confocal imaging, we have dissected multiple roles for the small GTPase Rac in this process. We show that constitutive activation of Rac1 leads to excessive assembly of lamellipodia and precocious halting of epithelial sweeping, possibly through premature activation of contact-inhibition machinery. Conversely, blocking Rac activity, either by loss-of-function mutations or expression of dominant negative Rac1, disables the assembly of both actin cable and protrusions by epithelial cells. Movies of mutant embryos show that continued contraction of the amnioserosa is sufficient to draw the epithelial edges towards one another, allowing the zipper machinery to bypass non-functioning regions of leading edge. In addition to illustrating the key role of Rac in organization of leading edge actin, loss-of-function mutants also provide substantive proof that Rac acts upstream in the Jun N-terminal kinase (JNK) cascade to direct epithelial cell shape changes during dorsal closure.

Animals↗
PubMed1999

Intermolecular interactions between dimeric calcium-sensing receptor monomers are important for its normal function.

We recently demonstrated that the G protein-coupled, extracellular calcium-sensing receptor (CaR) forms disulfide-linked dimers. The functional significance of dimerization of this receptor was suggested by our earlier observations that CaRs carrying certain point mutations exert dominant negative effects on the function of the coexpressed wild-type receptor both in vivo and when cotransfected in human embryonic kidney cells. In this study, we explored the functional consequences of CaR dimerization. Coexpression in human embryonic kidney cells of specific pairs of mutant CaRs, each with reduced or absent activity because of distinct loss-of-function mutations, results in the formation of heterodimers and partially reconstitutes extracellular calcium-dependent signaling. Moreover, our results suggest that the CaR has at least two functionally separable domains. However, the presence of an abnormal domain in each mutant monomer substantially impairs the function of the CaR heterodimer, resulting in the reconstituted CaRs having characteristics distinct from those of the wild-type CaR. Our study suggests that intermolecular interactions within the dimeric CaR are important for the receptor's function.

Calcium Signaling↗
PubMed2003

Fungal metabolic model for 3-methylcrotonyl-CoA carboxylase deficiency.

Aspergillus nidulans is able to use Leu as the sole carbon source through a metabolic pathway leading to acetyl-CoA and acetoacetate that is homologous to that used by humans. mccA and mccB, the genes encoding the subunits of 3-methylcrotonyl-CoA carboxylase, are clustered with ivdA encoding isovaleryl-CoA dehydrogenase, a third gene of the Leu catabolic pathway, on the left arm of chromosome III. Their transcription is induced by Leu and other hydrophobic amino acids and repressed by glucose. Phenotypically indistinguishable DeltamccA, DeltamccB, and DeltamccA DeltamccB mutations prevent growth on Leu but not on lactose or other amino acids, formally demonstrating in vivo the specific involvement of 3-methylcrotonyl-CoA carboxylase in Leu catabolism. Growth of mcc mutants on lactose plus Leu is impaired, indicating that Leu metabolite(s) accumulation resulting from the metabolic block is toxic. Human patients carrying loss-of-function mutations in the genes encoding the subunits of 3-methylcrotonyl-CoA carboxylase suffer from methylcrotonylglycinuria. Gas chromatography/mass spectrometry analysis of culture supernatants revealed that fungal Deltamcc strains accumulate 3-hydroxyisovaleric acid, one of the diagnostic compounds in the urine of these patients, illustrating the remarkably similar consequences of equivalent genetic errors of metabolism in fungi and humans. We use our fungal model(s) for methylcrotonylglycinuria to show accumulation of 3-hydroxyisovalerate on transfer of 3-methylcrotonyl-CoA carboxylase-deficient strains to the isoprenoid precursors acetate, 3-hydroxy-3-methylglutarate, or mevalonate. This represents the first reported genetic evidence for the existence of a metabolic link involving 3-methylcrotonyl-CoA carboxylase between isoprenoid biosynthesis and Leu catabolism, providing additional support to the mevalonate shunt proposed previously (Edmond, J., and Popják, G. (1974) J. Biol. Chem. 249, 66-71).

Alleles↗