Hydroxylation of demethoxy-Q6 constitutes a control point in yeast coenzyme Q6 biosynthesis

Coenzyme Q is a lipid molecule required for respiration and antioxidant protection. Q biosynthesis in Saccharomyces cerevisiae requires nine proteins (Coq1p-Coq9p). We demonstrate in this study that Q levels are modulated during growth by its conversion from demethoxy-Q (DMQ), a late intermediate. Similar conversion was produced when cells were subjected to oxidative stress conditions. Changes in Q(6)/DMQ(6) ratio were accompanied by changes in COQ7 gene mRNA levels encoding the protein responsible for the DMQ hydroxylation, the penultimate step in Q biosynthesis pathway. Yeast coq null mutant failed to accumulate any Q late biosynthetic intermediate. However, in coq7 mutants the addition of exogenous Q produces the DMQ synthesis. Similar effect was produced by over-expressing ABC1/COQ8. These results support the existence of a biosynthetic complex that allows the DMQ(6) accumulation and suggest that Coq7p is a control point for the Q biosynthesis regulation in yeast.

Yeast COQ4 encodes a mitochondrial protein required for coenzyme Q synthesis

The COQ4 gene coding for a component of the coenzyme Q biosynthetic pathway in the yeast Saccharomyces cerevisiae was cloned by a functional complementation of a Q-deficient mutant strain. Yeast coq4 mutant strains harboring the COQ4 gene on either single- or multicopy plasmids acquired the ability to grow on media containing a nonfermentable carbon source, synthesize Q(6), and respire. COQ4 encodes a polypeptide containing 335 amino acids with a calculated molecular mass of 38.6 kDa. By Western blot analysis with a specific antiserum, Coq4p was shown to peripherally associate with the matrix face of the mitochondrial inner membrane. The putative mitochondrial-targeting sequence present at the amino-terminus of the polypeptide efficiently imported it to mitochondria in a membrane-potential-dependent manner. Steady-state levels of COQ4 mRNA were increased during growth on glycerol-containing medium, in accordance with a function in Q biosynthesis. The function of Coq4p is unknown, although its presence is required to maintain a steady-state level of Coq7p, another component of the Q biosynthetic pathway. The results presented here, along with those available from literature, are discussed in light of the recently proposed existence of a multisubunit complex functioning in Q biosynthesis (A. Y. Hsu, T. Q. Do, P. T. Lee, and C. F. Clarke, 2000, Biochim. Biophys. Acta 1484, 287-297).

A defect in coenzyme Q biosynthesis is responsible for the respiratory deficiency in Saccharomyces cerevisiae abc1 mutants

Ubiquinone (coenzyme Q or Q) is an essential component of the mitochondrial respiratory chain in eukaryotic cells. There are eight complementation groups of Q-deficient Saccharomyces cerevisiae mutants designated coq1-coq8. Here we report that COQ8 is ABC1 (for Activity of bc(1) complex), which was originally isolated as a multicopy suppressor of a cytochrome b mRNA translation defect (Bousquet, I., Dujardin, G., and Slonimski, P. P. (1991) EMBO J. 10, 2023-2031). Previous studies of abc1 mutants suggested that the mitochondrial respiratory complexes were thermosensitive and function inefficiently. Although initial characterization of the abc1 mutants revealed characteristics of Q-deficient mutants, levels of Q were reported to be similar to wild type. The suggested function of Abc1p was that it acts as a chaperone-like protein essential for the proper conformation and functioning of the bc(1) and its neighboring complexes (Brasseur, G., Tron, P., Dujardin, G., Slonimski, P. P. (1997) Eur. J. Biochem. 246, 103-111). Studies presented here indicate that abc1/coq8 null mutants are defective in Q biosynthesis and accumulate 3-hexaprenyl-4-hydroxybenzoic acid as the predominant intermediate. As observed in other yeast coq mutants, supplementation of growth media with Q(6) rescues the abc1/coq8 null mutants for growth on nonfermentable carbon sources. Such supplementation also partially restores succinate-cytochrome c reductase activity in the abc1/coq8 null mutants. Abc1/Coq8p localizes to the mitochondria, and is proteolytically processed upon import. The findings presented here indicate that the previously reported thermosensitivity of the respiratory complexes of abc1/coq8 mutants results from the lack of Q and a general deficiency in respiration, rather than a specific phenotype due to dysfunction of the Abc1 polypeptide. These results indicate that ABC1/COQ8 is essential for Q-biosynthesis and that the critical defect of abc1/coq8 mutants is a lack of Q.

A dietary source of coenzyme Q is essential for growth of long-lived Caenorhabditis elegans clk-1 mutants

Mutations in the clk-1 gene of the nematode Caenorhabditis elegans result in slowed development, sluggish adult behaviors, and an increased lifespan. CLK-1 is a mitochondrial polypeptide with sequence and functional conservation from human to yeast. Coq7p, the Saccharomyces cerevisiae homologue, is essential for ubiquinone (coenzyme Q or Q) synthesis and therefore respiration. However, based on assays of respiratory function, it has been reported that the primary defect in the C. elegans clk-1 mutants is not in Q biosynthesis. How do the clk-1 mutant worms have essentially normal rates of respiration, when biochemical studies in yeast suggest a Q deficiency? Nematodes are routinely fed Escherichia coli strains containing a rich supply of Q. To study the Q synthesized by C. elegans, we cultured worms on an E. coli mutant that lacks Q and found that clk-1 mutants display early developmental arrest from eggs, or sterility emerging from dauer stage. Provision of Q-replete E. coli rescues these defects. Lipid analysis showed that clk-1 worms lack the nematode Q(9) isoform and instead contain a large amount of a metabolite that is slightly more polar than Q(9). The clk-1 mutants also have increased levels of Q(8), the E. coli isoform, and rhodoquinone-9. These results show that the clk-1 mutations result in Q auxotrophy evident only when Q is removed from the diet, and that the aging and developmental phenotypes previously described are consistent with altered Q levels and distribution.

Prevalence of coeliac disease and longitudinal follow-up of antigliadin antibody status in children and adolescents with type 1 diabetes mellitus

Coeliac disease (CD) is more prevalent in individuals with type 1 diabetes mellitus (DM), and when untreated is associated with a number of medical complications, including poor glycaemic control. Identification of patients with CD has been facilitated in recent years by serological screening, including the use of antigliadin antibodies (AGAs) and endomysial antibodies (EMAs). The aim of this study was to assess the prevalence of CD in a clinic-based paediatric population with type 1 DM, and to study longitudinal changes in AGA status. Two-hundred-and-eighty-one children and adolescents with type 1 DM aged 9.9 +/- 3.8 yr were screened using AGAs of immunoglobulin A (IgA) and immunoglobulin G (IgG) classes (AGA-IgA and AGA-IgG). Thirty-five patients had both antibodies positive and underwent gastro-duodenoscopy and multiple biopsies. Fifteen of the 35 patients had histological evidence of CD, and the overall clinic prevalence of CD was 5.7%. A number of patients did not exhibit florid symptoms, and recurrent unexplained hypoglycaemia was a significant finding. Patients who perceived themselves to be asymptomatic had more problems with compliance with a gluten-free diet (GFD). Ninety-seven patients had follow-up AGAs performed after 2.5 +/- 1.5 yr. One patient with initially normal AGAs developed positive antibodies and histological findings of CD. Antibody status has fluctuated in other patients. CD is common in patients with DM, and diagnosis is important to detect to minimize long-term morbidity related to both disorders. Initial normal screening does not exclude CD and repeat screening is indicated.

Identification of Escherichia coli ubiB, a gene required for the first monooxygenase step in ubiquinone biosynthesis

It was recently discovered that the aarF gene in Providencia stuartii is required for coenzyme Q (CoQ) biosynthesis. Here we report that yigR, the Escherichia coli homologue of aarF, is ubiB, a gene required for the first monooxygenase step in CoQ biosynthesis. Both the P. stuartii aarF and E. coli ubiB (yigR) disruption mutant strains lack CoQ and accumulate octaprenylphenol. Octaprenylphenol is the CoQ biosynthetic intermediate found to accumulate in the E. coli strain AN59, which contains the ubiB409 mutant allele. Analysis of the mutation in the E. coli strain AN59 reveals no mutations within the ubiB gene, but instead shows the presence of an IS1 element at position +516 of the ubiE gene. The ubiE gene encodes a C-methyltransferase required for the synthesis of both CoQ and menaquinone, and it is the 5' gene in an operon containing ubiE, yigP, and ubiB. The data indicate that octaprenylphenol accumulates in AN59 as a result of a polar effect of the ubiE::IS1 mutation on the downstream ubiB gene. AN59 is complemented by a DNA segment containing the contiguous ubiE, yigP, and ubiB genes. Although transformation of AN59 with a DNA segment containing the ubiB coding region fails to restore CoQ biosynthesis, transformation with the ubiE coding region results in a low-frequency but significant rescue attributed to homologous recombination. In addition, the fre gene, previously considered to correspond to ubiB, was found not to be involved in CoQ biosynthesis. The ubiB gene is a member of a predicted protein kinase family of which the Saccharomyces cerevisiae ABC1 gene is the prototypic member. The possible protein kinase function of UbiB and Abc1 and the role these polypeptides may play in CoQ biosynthesis are discussed.

Isolation and functional expression of human COQ3, a gene encoding a methyltransferase required for ubiquinone biosynthesis

The COQ3 gene in Saccharomyces cerevisiae encodes an O-methyltransferase required for two steps in the biosynthetic pathway of ubiquinone (coenzyme Q, or Q). This enzyme methylates an early Q intermediate, 3,4-dihydroxy-5-polyprenylbenzoic acid, as well as the final intermediate in the pathway, converting demethyl-Q to Q. This enzyme is also capable of methylating the distinct prokaryotic early intermediate 2-hydroxy-6-polyprenyl phenol. A full-length cDNA encoding the human homologue of COQ3 was isolated from a human heart cDNA library by sequence homology to rat Coq3. The clone contained a 933-base pair open reading frame that encoded a polypeptide with a great deal of sequence identity to a variety of eukaryotic and prokaryotic Coq3 homologues. In the region between amino acids 89 and 255 in the human sequence, the rat and human homologues are 87% identical, whereas human and yeast are 35% identical. When expressed in multicopy, the human construct rescued the growth of a yeast coq3 null mutant on a nonfermentable carbon source and restored coenzyme Q biosynthesis, although at lower levels than that of wild type yeast. In vitro methyltransferase assays using farnesylated analogues of intermediates in the coenzyme Q biosynthetic pathway as substrates showed that the human enzyme is active with all three substrates tested.

Genetic evidence for a multi-subunit complex in the O-methyltransferase steps of coenzyme Q biosynthesis

Coq3 O-methyltransferase carries out both O-methylation steps in coenzyme Q (ubiquinone) biosynthesis. The degree to which Coq3 O-methyltransferase activity and expression are dependent on the other seven COQ gene products has been investigated. A panel of yeast mutant strains harboring null mutations in each of the genes required for coenzyme Q biosynthesis (COQ1-COQ8) have been prepared. Mitochondria have been isolated from each member of the yeast coq mutant collection, from the wild-type parental strains and from respiratory deficient mutants harboring deletions in ATP2 or COR1 genes. These latter strains constitute Q-replete, respiratory deficient controls. Each of these mitochondrial preparations has been analyzed for COQ3-encoded O-methyltransferase activity and steady state levels of Coq3 polypeptide. The findings indicate that the presence of the other COQ gene products is required to observe normal levels of O-methyltransferase activity and the Coq3 polypeptide. However, COQ3 steady state RNA levels are not decreased in any of the coq mutants, relative to either wild-type or respiratory deficient control strains, suggesting either a decreased rate of translation or a decreased stability of the Coq3 polypeptide. These data are consistent with the involvement of the Coq polypeptides (or the Q-intermediates formed by the Coq polypeptides) in a multi-subunit complex. It is our hypothesis that a deficiency in any one of the COQ gene products results in a defective complex in which the Coq3 polypeptide is rendered unstable.

Ambulatory blood pressure, microalbuminuria, and autonomic neuropathy in adolescents with type 1 diabetes

OBJECTIVE

To examine the relationship between 24-h blood pressure (BP) measurements, urinary albumin excretion rates, and autonomic neuropathy (AN) in adolescents with type 1 diabetes.

RESEARCH DESIGN AND METHODS

A total of 31 patients with microalbuminuria (MA), 20 patients with intermittent MA (I-MA) and 11 patients with persistent MA (P-MA) were identified from the diabetes clinics at two major Australian tertiary care pediatric hospitals. Two control groups were used; one consisted of 19 age-, sex-, and diabetes duration-matched adolescents with normoalbuminuria (NA), and the other consisted of 46 age- and sex-matched nondiabetic control subjects. A medical history and physical examination were followed by a series of noninvasive tests of cardiovascular and pupillary autonomic function and then by 24-h ambulatory blood pressure monitoring (ABPM).

RESULTS

ABPM showed an incremental increase in all BP parameters from nondiabetic control subjects through subjects with NA. A parallel incremental increase in diurnal and nocturnal ambulatory heart rates was also evident. Subjects with MA had significantly reduced pupillary adaptation to darkness compared with nondiabetic subjects and subjects with NA. The above results paralleled an incremental increase in HbAlc levels in adolescents with type 1 diabetes from subjects with NA to subjects with P-MA.

CONCLUSIONS

Higher 24-h BP values and evidence of subclinical signs of AN are present before P-MA develops and may have important implications for timing the introduction of treatments designed to prevent or retard the microvascular complications of type 1 diabetes in adolescents.

Conservation of the Caenorhabditis elegans timing gene clk-1 from yeast to human: a gene required for ubiquinone biosynthesis with potential implications for aging

Mutations in the Caenorhabditis elegans gene clk-1 have a major effect on slowing development and increasing life span. The Saccharomyces cerevisiae homolog COQ7 encodes a mitochondrial protein involved in ubiquinone biosynthesis and, hence, is required for respiration and gluconeogenesis. In this study, RT-PCR and 5' RACE were used to isolate both human and mouse clk-1/COQ7 homologs. Human CLK-1 was mapped to Chr 16(p12-13.1) by Radiation Hybrid (RH) and fluorescence in situ hybridization (FISH) methods. The number and location of human CLK1 introns were determined, and the location of introns II and IV are the same as in C. elegans. Northern blot analysis showed that three different isoforms of CLK-1 mRNA are present in several tissues and that the isoforms differ in the amount of expression. The functional equivalence of human CLK-1 to the yeast COQ7 homolog was tested by introducing either a single or multicopy plasmid containing human CLK-1 cDNA into yeast coq7 deletion strains and assaying for growth on a nonfermentable carbon source. The human CLK-1 gene was able to functionally complement yeast coq7 deletion mutants. The protein similarities and the conservation of function of the CLK-1/clk-1/COQ7 gene products suggest a potential link between the production of ubiquinone and aging.

Yeast and rat Coq3 and Escherichia coli UbiG polypeptides catalyze both O-methyltransferase steps in coenzyme Q biosynthesis

Ubiquinone (coenzyme Q or Q) is a lipid that functions in the electron transport chain in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes. Q-deficient mutants of Saccharomyces cerevisiae harbor defects in one of eight COQ genes (coq1-coq8) and are unable to grow on nonfermentable carbon sources. The biosynthesis of Q involves two separate O-methylation steps. In yeast, the first O-methylation utilizes 3, 4-dihydroxy-5-hexaprenylbenzoic acid as a substrate and is thought to be catalyzed by Coq3p, a 32.7-kDa protein that is 40% identical to the Escherichia coli O-methyltransferase, UbiG. In this study, farnesylated analogs corresponding to the second O-methylation step, demethyl-Q(3) and Q(3), have been chemically synthesized and used to study Q biosynthesis in yeast mitochondria in vitro. Both yeast and rat Coq3p recognize the demethyl-Q(3) precursor as a substrate. In addition, E. coli UbiGp was purified and found to catalyze both O-methylation steps. Futhermore, antibodies to yeast Coq3p were used to determine that the Coq3 polypeptide is peripherally associated with the matrix-side of the inner membrane of yeast mitochondria. The results indicate that one O-methyltransferase catalyzes both steps in Q biosynthesis in eukaryotes and prokaryotes and that Q biosynthesis is carried out within the matrix compartment of yeast mitochondria.

Autonomic nerve function in adolescents with Type 1 diabetes mellitus: relationship to microalbuminuria

AIMS

Thirty adolescent patients with Type 1 diabetes mellitus and microalbuminuria were studied for evidence of early autonomic neuropathy.

METHODS

Using tests involving cardiovascular and pupillary reflexes, the adolescents were compared with a normoalbuminuric group of patients with diabetes, who were matched for age, sex, puberty and duration of diabetes.

RESULTS

There was an increased prevalence of autonomic nerve dysfunction in the patients with microalbuminuria. These patients had higher resting heart rates (86 beats/min in the microalbuminuric group vs. 77 beats/min in normoalbuminuric controls, P = 0.002), and impaired pupillary dilatation in darkness (pupillary diameter % 56.5% vs. 62.5%, P = 0.003). Patients with microalbuminuria also had poorer long term glycaemic control (mean HbA1C 8.7% vs. 7.8%, P = 0.002) and higher blood pressures (systolic 125 vs. 116 mmHg, P = 0.001; diastolic 69 vs. 62 mmHg, P = 0.0001; mean arterial pressure 90 vs. 83 mmHg, P = 0.002) than those with normal urinary albumin excretion.

CONCLUSIONS

Microalbuminuria and autonomic nerve dysfunction co-exist in patients with Type 1 DM. Longitudinal studies will determine whether these findings have implications for the identification of patients at higher risk of progression of early renal complications.

Angel trumpet lily poisoning in five adolescents: clinical findings and management

OBJECTIVE

To describe clinical features and management of Angel trumpet lily poisoning in adolescents.

METHODOLOGY

Case notes of five adolescent males who presented to the emergency department of a teaching hospital were reviewed.

RESULTS

All five boys ingested a mixture of coca-cola and a brew prepared by boiling the leaves and flowers of the plant. They presented to the emergency department with various degrees of agitation and confusion and specific clinical signs. All were treated with charcoal and cathartics and discharged after 36 h.

CONCLUSIONS

Due to its hallucinogenic effects, abuse of Angel trumpet lily is not uncommon and should be suspected in adolescents presenting with altered mental state and hallucinations in conjunction with other anticholinergic symptoms and signs.

Characterization of Saccharomyces cerevisiae ubiquinone-deficient mutants

Ubiquinol (QH2) is a lipid-soluble molecule that participates in cellular redox reactions. Previous studies have shown that yeast mutants lacking QH2 are hypersensitive to treatment with polyunsaturated fatty acids (PUFAs) indicating that QH2 can function as an antioxidant in vivo. In this study the effect of 1 mM linolenic acid on levels of Q6 and Q6H2 is assessed in both wild-type and respiration-deficient (atp2 delta) strains. The response of Q-deficient mutants to other forms of oxidative stress is further characterized to define those conditions where QH2 acts as an antioxidant. Endogenous antioxidant defense systems were also assessed in wild-type, Q-deficient, and atp2 delta strains. Superoxide dismutase (SOD) activity decreased and catalase activity increased in both Q-deficient and atp2 delta mutants compared to wild-type cells, suggesting that such changes result from the loss of respiration rather than the lack of Q.

Genetic evidence for coenzyme Q requirement in plasma membrane electron transport

Plasma membranes isolated from wild-type Saccharomyces cerevisiae crude membrane fractions catalyzed NADH oxidation using a variety of electron acceptors, such as ferricyanide, cytochrome c, and ascorbate free radical. Plasma membranes from the deletion mutant strain coq3delta, defective in coenzyme Q (ubiquinone) biosynthesis, were completely devoid of coenzyme Q6 and contained greatly diminished levels of NADH-ascorbate free radical reductase activity (about 10% of wild-type yeasts). In contrast, the lack of coenzyme Q6 in these membranes resulted in only a partial inhibition of either the ferricyanide or cytochrome-c reductase. Coenzyme Q dependence of ferricyanide and cytochrome-c reductases was based mainly on superoxide generation by one-electron reduction of quinones to semiquinones. Ascorbate free radical reductase was unique because it was highly dependent on coenzyme Q and did not involve superoxide since it was not affected by superoxide dismutase (SOD). Both coenzyme Q6 and NADH-ascorbate free radical reductase were rescued in plasma membranes derived from a strain obtained by transformation of the coq3delta strain with a single-copy plasmid bearing the wild type COQ3 gene and in plasma membranes isolated form the coq3delta strain grown in the presence of coenzyme Q6. The enzyme activity was inhibited by the quinone antagonists chloroquine and dicumarol, and after membrane solubilization with the nondenaturing detergent Zwittergent 3-14. The various inhibitors used did not affect residual ascorbate free radical reductase of the coq3delta strain. Ascorbate free radical reductase was not altered significantly in mutants atp2delta and cor1delta which are also respiration-deficient but not defective in ubiquinone biosynthesis, demonstrating that the lack of ascorbate free radical reductase in coq3delta mutants is related solely to the inability to synthesize ubiquinone and not to the respiratory-defective phenotype. For the first time, our results provide genetic evidence for the participation of ubiquinone in NADH-ascorbate free radical reductase, as a source of electrons for transmembrane ascorbate stabilization.

Coenzyme Q6 and iron reduction are responsible for the extracellular ascorbate stabilization at the plasma membrane of Saccharomyces cerevisiae

Yeast plasma membrane contains an electron transport system that maintains ascorbate in its reduced form in the apoplast. Reduction of ascorbate free radical by this system is comprised of two activities, one of them dependent on coenzyme Q6 (CoQ6). Strains with defects in CoQ6 synthesis exhibit decreased capacity for ascorbate stabilization compared with wild type or with atp2 or cor1 respiratory-deficient mutant strains. Both CoQ6 content in plasma membranes and ascorbate stabilization were increased during log phase growth. The addition of exogenous CoQ6 to whole cells resulted in its incorporation in the plasma membrane, produced levels of CoQ6 in the coq3 mutant strain that were 2-fold higher than in the wild type, and increased ascorbate stabilization activity in both strains, although it was higher in the coq3 mutant than in wild type. Other antioxidants, such as benzoquinone or alpha-tocopherol, did not change ascorbate stabilization. The CoQ6-independent reduction of ascorbate free radical was not due to copper uptake, pH changes or to the presence of CoQ6 biosynthetic intermediates, but decreased to undetectable levels when coq3 mutant strains were cultured in media supplemented with ferric iron. Plasma membrane CoQ6 levels were unchanged by either the presence or absence of iron in wild type, atp2, or cor1 strains. Ascorbate stabilization appears to be a function of the yeast plasma membrane, which is partially based on an electron transfer chain in which CoQ6 is the central electron carrier, whereas the remainder is independent of CoQ6 and other antioxidants but is dependent on the iron-regulated ferric reductase complex.

Yeast Clk-1 homologue (Coq7/Cat5) is a mitochondrial protein in coenzyme Q synthesis

Mutations in the clk-1 gene result in slower development and increased life span in Caenorhabditis elegans. The Saccharomyces cerevisiae homologue COQ7/CAT5 is essential for several metabolic pathways including ubiquinone biosynthesis, respiration, and gluconeogenic gene activation. We show here that Coq7p/Cat5p is a mitochondrial inner membrane protein directly involved in ubiquinone biosynthesis, and that the defect in gluconeogenic gene activation in coq7/cat5 null mutants is a general consequence of a defect in respiration. These results obtained in the yeast model suggest that the effects on development and life span in C. elegans clk-1 mutants may relate to changes in the amount of ubiquinone, an essential electron transport component and a lipid soluble antioxidant.

Progression of borderline increases in albuminuria in adolescents with insulin-dependent diabetes mellitus

We aimed to determine the natural history of borderline increases in albuminuria in adolescents with insulin-dependent (Type 1) diabetes mellitus (IDDM) and factors which are associated with progression to persistent microalbuminura. Fifty-five normotensive adolescents with IDDM and intermittent microalbuminura (overnight albumin excretion ratte of 20-200 micrograms min-1 on one of three consecutive timed collections, n = 29) or borderline albuminura (mean overnight albumin excretion rate of 7.2-20 micrograms min-1 on one of three consecutive timed collections, n = 30) were followed prospectively at 3 monthly intervals. The endpoint was persistent microalbuminuria defined as a minimum of three of four consecutive overnight albumin excretion rates of greater than 20 micrograms min-1. One hundred and forty-two adolescents with IDDM and normoalbuminura were also followed prospectively. Fifteen of the 59 patients (25.4%) with intermittent (9/29) or borderline (6/30) albuminura progressed to persistent microalbuminura (progressors) over 28 (15-50) months [median (range)] in comparison with two of the 142 patients with normoalbuminuria at entry (relative risk = 12.6; p = 0.001). Progressors to persistent microalbuminura were pubertal and had higher systolic (p = 0.02) and diastolic (p = 0.02) blood pressure, and HbA1c (p = 0.004) than non-progressors. All patients remained normotensive. Glomerular filtration rate, apolipoproteins, dietary phosphorus, protein and sodium intakes, and prevalence of smoking did not differ between progressors and non-progressors. Total renin was higher in the diabetic patients without a difference between progressors and non-progressors. In conclusion there is a relatively high rate of progression to persistent microalbuminuria in pubertal adolescents with borderline increases in albuminura and duration greater than 3 years. These patients require attention to minimize associated factors of poor metabolic control and higher blood pressure in the development of incipient nephropathy.

Characterization of the COQ5 gene from Saccharomyces cerevisiae. Evidence for a C-methyltransferase in ubiquinone biosynthesis

Ubiquinone (coenzyme Q or Q) is a lipophilic metabolite that functions in the electron transport chain in the plasma membrane of prokaryotes and in the inner mitochondrial membrane of eukaryotes. Q-deficient mutants of Saccharomyces cerevisiae fall into eight complementation groups (coq1-coq8). Yeast mutants from the coq5 complementation group lack Q and as a result are respiration-defective and fail to grow on nonfermentable carbon sources. A nuclear gene, designated COQ5 was isolated from a yeast genomic library based on its ability to restore growth of a representative coq5 mutant on media containing glycerol as the sole carbon source. The DNA segment responsible for the complementation contained an open reading frame (GenBankTM accession number Z49210Z49210) with 44% sequence identity over 262 amino acids to UbiE, which is required for a C-methyltransferase step in the Q and menaquinone biosynthetic pathways in Escherichia coli. Both the ubiE and COQ5 coding sequences contain sequence motifs common to a wide variety of S-adenosyl-L-methionine-dependent methyltransferases. A gene fusion expressing a biotinylated form of Coq5p retains function, as assayed by the complementation of the coq5 mutant. This Coq5-biotinylated fusion protein is located in mitochondria. The synthesis of two farnesylated analogs of intermediates in the ubiquinone biosynthetic pathway is reported. These reagents have been used to develop in vitro C-methylation assays with isolated yeast mitochondria. These studies show that Coq5p is required for the C-methyltransferase step that converts 2-methoxy-6-polyprenyl-1, 4-benzoquinone to 2-methoxy-5-methyl-6-polyprenyl-1,4-benzoquinone.

Caring for the terminally ill adolescent

Terminally ill adolescents, a heterogeneous group, face unique problems in coming to terms with the prospect of death and dying. In parallel, the psychosocial sequelae of a terminal illness in the adolescent, and their effects on the family and health professionals, present unique challenges for management. Using a developmental framework, we examine issues surrounding the care of dying adolescents and present strategies for their management.

A C-methyltransferase involved in both ubiquinone and menaquinone biosynthesis: isolation and identification of the Escherichia coli ubiE gene

Strains of Escherichia coli with mutations in the ubiE gene are not able to catalyze the carbon methylation reaction in the biosynthesis of ubiquinone (coenzyme Q) and menaquinone (vitamin K2), essential isoprenoid quinone components of the respiratory electron transport chain. This gene has been mapped to 86 min on the chromosome, a region where the nucleic acid sequence has recently been determined. To identify the ubiE gene, we evaluated the amino acid sequences encoded by open reading frames located in this region for the presence of sequence motifs common to a wide variety of S-adenosyl-L-methionine-dependent methyltransferases. One open reading frame in this region (o251) was found to encode these motifs, and several lines of evidence that confirm the identity of the o251 product as UbiE are presented. The transformation of a strain harboring the ubiE401 mutation with o251 on an expression plasmid restored both the growth of this strain on succinate and its ability to synthesize both ubiquinone and menaquinone. Disruption of o251 in a wild-type parental strain produced a mutant with defects in growth on succinate and in both ubiquinone and menaquinone synthesis. DNA sequence analysis of the ubiE401 allele identified a missense mutation resulting in the amino acid substitution of Asp for Gly142. E. coli strains containing either the disruption or the point mutation in ubiE accumulated 2-octaprenyl-6-methoxy-1,4-benzoquinone and demethylmenaquinone as predominant intermediates. A search of the gene databases identified ubiE homologs in Saccharomyces cerevisiae, Caenorhabditis elegans, Leishmania donovani, Lactococcus lactis, and Bacillus subtilis. In B. subtilis the ubiE homolog is likely to be required for menaquinone biosynthesis and is located within the gerC gene cluster, known to be involved in spore germination and normal vegetative growth. The data presented identify the E. coli UbiE polypeptide and provide evidence that it is required for the C methylation reactions in both ubiquinone and menaquinone biosynthesis.

Sensitivity to treatment with polyunsaturated fatty acids is a general characteristic of the ubiquinone-deficient yeast coq mutants

The biosynthesis of ubiquinone (Q) and the functional consequences of Q-deficiency was studied in the yeast Saccharomyces cerevisiae. Lipid extracts were prepared from various respiratory deficient mutants grown in the presence of p-[U-14C]hydroxybenzoic acid. Q mutant strains harboring mutations in the coq3, coq4, coq5, coq6, coq7, or coq8 genes were unable to produce Q and accumulated an early intermediated that corresponded to 3-hexaprenyl-4-hydroxybenzoic acid. Several respiratory deficient yeast including both nuclear and mitochondrial petite mutant strains, retain the ability to produce Q. Thus, the inability to produce Q is a specific phenotype manifested in the class of mutants termed 'coq'. Previous studies described the enhanced sensitivity of the Q-deficient yeast strain containing a deletion in the COQ3 gene to the products of autoxidized polyunsaturated fatty acids (Do et al., 1996, Proceeding of the National Academy of Science USA, 93, 7534-7539). The results presented here show this to be a general phenotype resulting from Q-deficiency, as all of the coq mutant yeast strains tested exhibit hypersensitivity to polyunsaturated fatty acid treatment.

Complementation of coq3 mutant yeast by mitochondrial targeting of the Escherichia coli UbiG polypeptide: evidence that UbiG catalyzes both O-methylation steps in ubiquinone biosynthesis

Ubiquinone functions in the mitochondrial electron transport chain. Recent evidence suggests that the reduced form of ubiquinone (ubiquinol) may also function as a lipid soluble antioxidant. The biosynthesis of ubiquinone requires two O-methylation steps. In eukaryotes, the first O-methylation step is carried out by the Coq3 polypeptide, which catalyzes the transfer of a methyl group from S-adenosylmethionine to 3,4-dihydroxy-5-polyprenylbenzoate. In Escherichia coli, 2-polyprenyl-6-hydroxyphenol is the predicted substrate; however, the corresponding O-methyltransferase has not been identified. The second O-methylation step in E. coli, the conversion of demethylubiquinone to ubiquinone, is carried out by the UbiG methyltransferase, which is 40% identical in amino acid sequence with the yeast Coq3 methyltransferase. On the basis of the chemical similarity of the first and last methyl-acceptor substrates and the high degree of amino acid sequence identity between Coq3p and UbiG, the ability of UbiG to catalyze both O-methylation steps was investigated. The current study shows that the ubiG gene is able to restore respiration in the yeast coq3 mutant, provided ubiG is modified to contain a mitochondrial leader sequence. The mitochondrial targeting of O-methyltransferase activity is an essential feature of the ability to restore respiration and hence ubiquinone biosynthesis in vivo. In vitro import assays show the mitochondrial leader sequence present on Coq3p functions to direct mitochondrial import of Coq3p in vitro and that processing to the mature form requires a membrane potential. In vitro methyltransferase assays with E. coli cell lysates and synthetically prepared farnesylated-substrate analogs indicate that UbiG methylates both the derivative of the eukaryotic intermediate, 3,4-dihydroxy-5-farnesylbenzoate, as well as that of the E. coli intermediate, 2-farnesyl-6-hydroxyphenol. The data presented indicate that the yeast Coq3 polypeptide is located in the mitochondria and that E. coli UbiG catalyzes both O-methylation steps in E. coli.

Enhanced sensitivity of ubiquinone-deficient mutants of Saccharomyces cerevisiae to products of autoxidized polyunsaturated fatty acids

Coenzyme Q (ubiquinone or Q) plays a well known electron transport function in the respiratory chain, and recent evidence suggests that the reduced form of ubiquinone (QH2) may play a second role as a potent lipid-soluble antioxidant. To probe the function of QH2 as an antioxidant in vivo, we have made use of a Q-deficient strain of Saccharomyces cerevisiae harboring a deletion in the COQ3 gene [Clarke, C. F., Williams, W. & Teruya, J. H. (1991) J. Biol. Chem. 266, 16636-16644]. Q-deficient yeast and the wild-type parental strain were subjected to treatment with polyunsaturated fatty acids, which are prone to autoxidation and breakdown into toxic products. In this study we find that Q-deficient yeast are hypersensitive to the autoxidation products of linolenic acid and other polyunsaturated fatty acids. In contrast, the monounsaturated oleic acid, which is resistant to autoxidative breakdown, has no effect. The hypersensitivity of the coq3delta strains can be prevented by the presence of the COQ3 gene on a single copy plasmid, indicating that the sensitive phenotype results solely from the inability to produce Q. As a result of polyunsaturated fatty acid treatment, there is a marked elevation of lipid hydroperoxides in the coq3 mutant as compared with either wild-type or respiratory-deficient control strains. The hypersensitivity of the Q-deficient mutant can be rescued by the addition of butylated hydroxytoluene, alpha-tocopherol, or trolox, an aqueous soluble vitamin E analog. The results indicate that autoxidation products of polyunsaturated fatty acids mediate the cell killing and that QH2 plays an important role in vivo in protecting eukaryotic cells from these products.

Isolation and sequencing of the rat Coq7 gene and the mapping of mouse Coq7 to chromosome 7

We recently identified the Saccharomyces cerevisiae COQ7 gene and showed that its product affects one or more monoxygenase steps in the synthesis of ubiquinone. Other investigators have independently isolated the yeast COQ7 gene as CAT5 and identified it as a gene necessary for the derepression of gluconeogenic enzymes in yeast. In the present study, a homolog of the yeast COQ7 (CAT5) gene was isolated from a rat testis cDNA library by functional complementation of a coq7 deletion mutant of S. cerevisiae. The resulting cDNA clones contained a 0.8-kb insert with an open reading frame encoding a 183-amino-acid polypeptide. The rat Coq7 amino acid sequence is 49% identical to that of yeast Coq7p and 58% identical to a C. elegans homolog over a 152-aa region. Sequence homology searches fail to identify any other significant homologies. The Coq7 gene was mapped to mouse chromosome 7, 7.6 +/- 3.6 cM proximal to the marker D7Mit7, by linkage analysis of an interspecific backcross. This region of chromosome 7 containing Coq7 is part of a linkage group conserved between mouse chromosome 7 and human chromosome 11p15.

Autoxidation of ubiquinol-6 is independent of superoxide dismutase

Ubiquinone (Q) is an essential, lipid soluble, redox component of the mitochondrial respiratory chain. Much evidence suggests that ubiquinol (QH2) functions as an effective antioxidant in a number of membrane and biological systems by preventing peroxidative damage to lipids. It has been proposed that superoxide dismutase (SOD) may protect QH2 form autoxidation by acting either directly as a superoxide-semiquinone oxidoreductase or indirectly by scavenging superoxide. In this study, such an interaction between QH2 and SOD was tested by monitoring the fluorescence of cis-parinaric acid (cPN) incorporated phosphatidylcholine (PC) liposomes. Q6H2 was found to prevent both fluorescence decay and generation of lipid peroxides (LOOH) when peroxidation was initiated by the lipid-soluble azo initiator DAMP, dimethyl 2,2'-azobis (2-methylpropionate), while Q6 or SOD alone had no inhibitory effect. Addition of either SOD or catalase to Q6H2-containing liposomes had little effect on the rate of peroxidation even when incubated in 100% O2. Hence, the autoxidation of QH2 is a competing reaction that reduces the effectiveness of QH2 as an antioxidant and was not slowed by either SOD or catalase. The in vivo interaction of SOD and QH2 was also tested by employing yeast mutant strains harboring deletions in either CuZnSOD and/or MnSOD. The sod mutant yeast strains contained the same percent Q6H2 per cell as wild-type cells. These results indicate that the autoxidation of QH2 is independent of SOD.

The COQ7 gene encodes a protein in saccharomyces cerevisiae necessary for ubiquinone biosynthesis

Ubiquinone (coenzyme Q) is a lipid that transports electrons in the respiratory chains of both prokaryotes and eukaryotes. Mutants of Saccharomyces cerevisiae deficient in ubiquinone biosynthesis fail to grow on nonfermentable carbon sources and have been classified into eight complementation groups (coq1 coq8; Tzagoloff, A., and Dieckmann, C. L.(1990) Microbiol. Rev. 54, 211-225). In this study we show that although yeast coq7 mutants lack detectable ubiquinone, the coq7 1 mutant does synthesize demethoxyubiquinone (2-hexaprenyl-3-methyl-6-methoxy-1,4-benzoquinone), a ubiquinone biosynthetic intermediate. The corresponding wild-type COQ7 gene was isolated, sequenced, and found to restore growth on nonfermentable carbon sources and the synthesis of ubiquinone. The sequence predicts a polypeptide of 272 amino acids which is 40% identical to a previously reported Caenorhabditis elegans open reading frame. Deletion of the chromosomal COQ7 gene generates respiration defective yeast mutants deficient in ubiquinone. Analysis of several coq7 deletion strains indicates that, unlike the coq7 1 mutant, demethoxyubiquinone is not produced. Both coq7 1 and coq7 deletion mutants, like other coq mutants, accumulate an early intermediate in the ubiquinone biosynthetic pathway, 3-hexaprenyl-4-hydroxybenzoate. The data suggest that the yeast COQ7 gene may encode a protein involved in one or more monoxygenase or hydroxylase steps of ubiquinone biosynthesis.

3-Hexaprenyl-4-hydroxybenzoic acid forms a predominant intermediate pool in ubiquinone biosynthesis in Saccharomyces cerevisiae

The biosynthesis of ubiquinone (coenzyme Q) was studied in Saccharomyces cerevisiae. Lipid extracts were prepared from wild-type yeast grown in the presence of p-[U-14C]- and p-[carboxy-14C]hydroxybenzoic acid. Ergosterol was removed by adsorption to digitonin-celite, and radiolabeled lipids were purified by sequential reverse-phase and normal-phase HPLC steps. Radiolabeled peaks were identified by comparison with synthetic standards using retention time and electron ionization mass spectrometric criteria. The recovery and identification of the unstable 3-hexaprenyl-4-hydroxybenzoic acid molecule were facilitated by treatment of the lipid extract with diazomethane under conditions that resulted in the formation of the stable derivatives methyl 3-hexaprenyl-4-hydroxybenzoate or methyl 3-hexaprenyl-4-methoxybenzoate. In stationary-phase yeast cultures, the major radioactive lipid products are coenzyme Q and 3-hexaprenyl-4-hydroxybenzoic acid, constituting 62 and 38% of the radioactive lipids, respectively. However, under log-phase growth conditions the biosynthetic intermediate 3-hexaprenyl-4-hydroxybenzoic acid predominates (accounting for 81% of the radioactive lipids). The data indicate that in wild-type yeast, 3-hexaprenyl-4-hydroxybenzoic acid forms a predominant intermediate pool in ubiquinone biosynthesis and that in log-phase growth this ubiquinone intermediate is present at fourfold higher abundance than the end product. The physiological rationale for this high concentration of a membrane-bound intermediate is unclear.

Ubiquinone biosynthesis in eukaryotic cells: tissue distribution of mRNA encoding 3,4-dihydroxy-5-polyprenylbenzoate methyltransferase in the rat and mapping of the COQ3 gene to mouse chromosome 4

The isolation and sequence of a rat cDNA corresponding to the rat COQ3 gene was recently reported. The COQ3 gene encodes 3,4-dihydroxy-5-polyprenylbenzoate methyltransferase, an enzyme in coenzyme Q biosynthesis. In this study, the rat COQ3 cDNA has been used to examine the expression and chromosomal localization of the COQ3 gene. COQ3 mRNA was detected in every tissue analyzed, consistent with the idea that in most tissues de novo synthesis accounts for the observed levels of Q. Highest levels were present in testis, heart, and skeletal muscle. The rat COQ3 cDNA hybridized to genomic DNA from multiple species, suggesting the conserved nature of the 3,4-dihydroxy-5-polyprenylbenzoate methyltransferase. A single copy of the COQ3 gene appears to be present in rats and mice. By analyzing a restriction fragment length variant in an interspecific backcross, the COQ3 gene was localized to mouse chromosome 4, at a position 3.7 +/- 2.6 cM proximal to the marker D4Mit4. The map position of the gene, designated Coq3, places it in close proximity to the mouse vacillans or vc mutation. The symptoms exhibited by the vc mice are similar to those reported for Q deficiencies in humans.

Cloning of a rat cDNA encoding dihydroxypolyprenylbenzoate methyltransferase by functional complementation of a Saccharomyces cerevisiae mutant deficient in ubiquinone biosynthesis

3,4-Dihydroxy-5-hexaprenylbenzoate methyltransferase (DHHB-MTase) is the product of the COQ3 gene in Saccharomyces cerevisiae and catalyses the fourth step in the biosynthesis of ubiquinone (coenzyme Q) from p-hydroxybenzoic acid. A full-length cDNA encoding a mammalian homologue of DHHB-MTase was isolated from a newly constructed rat testis cDNA library by functional complementation of a coq3 deletion mutant of S. cerevisiae. The complementing clone contained a 1.1-kb poly(A)(+)-tailed insert with a 858-bp open reading frame and presumably encodes 3,4-dihydroxy-5-polyprenylbenzoate-MTase. The deduced rat amino acid (aa) sequence has a 39% identity over 138 aa with the yeast DHHB-MTase and a 37% identity over this same region with an Escherichia coli protein encoded by the ubiG gene, a MTase that catalyses the terminal step of ubiquinone biosynthesis. The rescue of the yeast coq3 mutant by the rat homologue suggests that yeast and rat synthesize ubiquinone via the same early steps in this pathway.

Ubiquinone biosynthesis in Saccharomyces cerevisiae. Isolation and sequence of COQ3, the 3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase gene

Ubiquinone (or coenzyme Q) is a lipid component of the respiratory chain in the inner mitochondrial membrane, in which it functions in electron transport. Recent reports show that ubiquinone and ubiquinone biosynthetic enzymes are present in both mitochondrial and nonmitochondrial membranes of cells (Kalen, A., Appelkvist, E.-L., Chojnacki, T., and Dallner, G. (1990) J. Biol. Chem. 265, 1158-1164) although the functions that ubiquinone may play outside of the mitochondrion are not understood. To study coenzyme Q synthesis and function we cloned the 3,4-dihydroxy-5-hexaprenylbenzoate (DHHB) methyltransferase gene by functional complementation of a yeast coenzyme Q mutant strain, defective in the COQ3 gene (Tzagoloff, A., and Dieckmann, C. L. (1990) Microbiol. Rev. 54, 211-225). This gene restores both coenzyme Q synthesis in the mutant strain and the ability to grow on media containing glycerol, a nonfermentable substrate. A one-step in situ gene replacement with the cloned DHHB methyltransferase DNA directs integration to the yeast COQ3 locus on chromosome XV of Saccharomyces cerevisiae, establishing that the COQ3 locus encodes the DHHB methyltransferase structural gene. The predicted amino acid sequence of the yeast DHHB methyltransferase contains a methyltransferase consensus sequence and shows a 40% identity with an open reading frame of Escherichia coli, the gyrA5' hypothetical protein. This open reading frame is adjacent to the gyrA gene and close to the mapped location of the ubiG gene at 48 min on the E. coli chromosome. These results suggest that the E. coli gyrA5' open reading frame encodes a methyltransferase and may correspond to the ubiG gene, which is required for ubiquinone biosynthesis.

Testis-specific transcripts of rat farnesyl pyrophosphate synthetase are developmentally regulated and localized to haploid germ cells

A rat farnesyl pyrophosphate (FPP) synthetase cDNA was used to study the expression of FPP synthetase mRNA levels during spermatogenesis in the rat. RNA blot analysis showed an increase in the level of FPP synthetase transcripts during postnatal development of rat testes. The increase is due to the appearance of longer testis-specific FPP synthetase transcripts as assayed by primer extension mapping. In situ hybridization analysis of adult rat testis sections with an FPP synthetase antisense probe showed that FPP synthetase mRNA levels are greatly enriched in the haploid round spermatidis at stages 7 to 8 of the seminiferous epithelium. These results show that FPP synthetase transcripts in testis are expressed at high levels in haploid male germ cells in a stage-specific manner.

Testis-specific transcription initiation sites of rat farnesyl pyrophosphate synthetase mRNA

A variety of rat tissues were screened at low stringency with a rat farnesyl pyrophosphate (FPP) synthetase cDNA. In testis, an FPP synthetase-related RNA was detected that was larger than the liver FPP synthetase mRNA and was present at very high levels comparable with liver FPP synthetase RNA levels obtained from rats fed diets supplemented with cholestyramine and mevinolin. Sequence analysis of testis cDNA clones, together with primer extension and S1 nuclease experiments, indicated that testis FPP synthetase transcripts contain an extended 5' untranslated region. The 5' extension contained one or two out-of-frame upstream ATGs, depending on the site of transcription initiation. Protein in vitro translation studies indicated that the extended 5' untranslated region may play a role in regulating the translation of the FPP synthetase polypeptide in rat testis. Southern blot analysis with a probe containing both testis and liver 5' untranslated sequences provided evidence that both liver and testis transcripts derive from the same gene. The data suggest that an upstream testis-specific promoter results in the abundant production of FPP synthetase transcripts that are translated at low efficiency; another promoter functions in liver and other somatic tissues and directs the regulated synthesis of shorter discrete transcripts.

Limited joint mobility in children and adolescents with insulin dependent diabetes mellitus

Joint mobility was studied in 70 children with insulin dependent diabetes mellitus aged 8-17 years, and the prevalence of limited joint mobility (LJM) was found to be 31% (22/70). This figure fell to only 7% (5/70) when an alternative method of assessment was used. A high number of non-diabetic, non-sibling controls (6/51 (12%] were found to have LJM. There was a trend towards an increasing prevalence of LJM with increasing age and duration of diabetes, but it was also found in patients with recent onset diabetes. A large proportion of prepubertal patients were noted to have LJM. No correlation was found between LJM and either short stature or diabetic control. There is a need for standardisation of the methods used to define and stage LJM in diabetic patients, and the significance of this clinical finding remains unclear.

Pupillary size in children and adolescents with type 1 diabetes

Pupillary adaptation to darkness was studied in 63 children and adolescents with Type 1 diabetes using a simple portable pupillometer. Results were compared with those in a group of age-related non-diabetic children and expressed as the ratio of the pupil diameter to the iris diameter (pupil diameter %). In the diabetic patients the pupil diameter % was 61.1 +/- 5.8 (44.4-71.9) % compared with 64.2 +/- 4.1 (53.2-72.6) % in the control subjects (p less than 0.001). Abnormal pupillary adaptation to darkness was found more commonly than abnormal heart rate variation in response to a variety of stimuli in the diabetic patients. Pupillary adaptation to darkness may be useful as an indicator of subclinical autonomic neuropathy in diabetic children.

Dispersed family of human genes with sequence similarity to farnesyl pyrophosphate synthetase

Prenyltransferases are a group of enzymes involved in the biosynthesis of both sterol and nonsterol isoprene compounds. Somatic cell hybrid studies and in situ hybridization show that the human genome contains five distinct loci that hybridize to the cDNA for the enzyme farnesyl pyrophosphate synthetase (FPS), a prenyltransferase that catalyzes the synthesis of an intermediate common to both the sterol and the nonsterol branches of the isoprene biosynthetic pathway. The loci identified in this report may correspond to unique prenyltransferase genes related to FPS or to pseudogenes. The loci mapped have been identified as farnesyl pyrophosphate synthetase-"like"-1 (FPSL-1) on chromosome 1q24-31, FPSL-2 on chromosome 7, FPSL-3 on chromosome 14, FPSL-4 on chromosome 15q14-q21, and FPSL-5 on chromosome Xq21-22. Multiple copies of sequences similar to those of FPS are also present in both the mouse and the rat.

Polycystic ovary syndrome in a virilised, premenarcheal girl

A premenarcheal girl aged 12 years presented with an abdominopelvic mass and virilisation. A large ovarian cyst was removed at laparotomy. A histological diagnosis of polycystic ovarian syndrome was made, with no evidence of an associated masculinising tumour.

Deliberate self poisoning in adolescents

A retrospective study of 90 adolescents admitted to a district general hospital after deliberate drug overdoses was carried out. Underlying risk factors, the inpatient assessment, and the initial management offered to each patient were recorded. The longer term outcomes were assessed, with particular emphasis on psychiatric and related disorders. Many had underlying family problems; the parents of nearly half the patients were separated or divorced, and over half the families had already been seen by the social services or at the child guidance clinic. Three quarters of the patients had psychiatric assessments during admission, and of these 59 (66%) were referred for further psychiatric treatment. Of these over half withdrew from treatment. Eleven (12%) of the children took a further drug overdose. This study emphasises the need for psychiatric assessment and treatment in these children, but the results suggest that the success of management is limited by poor patient compliance.

Purification of complexes of nuclear oncogene p53 with rat and Escherichia coli heat shock proteins: in vitro dissociation of hsc70 and dnaK from murine p53 by ATP

Oligomeric protein complexes containing the nuclear oncogene p53 and the simian virus 40 large tumor antigen (D. I. H. Linzer and A. J. Levine, Cell 17:43-51, 1979), the adenovirus E1B 55-kilodalton (kDa) tumor antigen, and the heat shock protein hsc70 (P. Hinds, C. Finlay, A. Frey, and A. J. Levine, Mol. Cell. Biol. 7:2863-2869, 1987) have all been previously described. To begin isolating, purifying, and testing these complexes for functional activities, we have developed a rapid immunoaffinity column purification. p53-protein complexes are eluted from the immunoaffinity column by using a molar excess of a peptide comprising the epitope recognized by the p53 monoclonal antibody. This mild and specific elution condition allows p53-protein interactions to be maintained. The hsc70-p53 complex from rat cells is heterogeneous in size, with some forms of this complex associated with a 110-kDa protein. The maximum apparent molecular mass of such complexes is 660,000 daltons. Incubation with micromolar levels of ATP dissociates this complex in vitro into p53 and hsc70 110-kDa components. Nonhydrolyzable substrates of ATP fail to promote this dissociation of the complex. Murine p53 synthesized in Escherichia coli has been purified 660-fold on the same antibody affinity column and was found to be associated with an E. coli protein of 70 kDa. Immunoblot analysis with specific antisera demonstrated that this E. coli protein was the heat shock protein dnaK, which has extensive sequence homology with the rat hsc70 protein. Incubation of the immunopurified p53-dnaK complex with ATP resulted in the dissociation of the p53-dnaK complex as it did with the p53-hsc70 complex. This remarkable conservation of p53-heat shock protein interactions and the specificity of dissociation reactions suggest a functionally important role for heat shock proteins in their interactions with oncogene proteins.

Molecular cloning and sequence of a cholesterol-repressible enzyme related to prenyltransferase in the isoprene biosynthetic pathway

Differential hybridization and molecular cloning have been used to isolate CR39, a cDNA which hybridizes to a 1.2-kilobase (kb) mRNA in rat liver. The level of CR39 mRNA was increased seven- to ninefold over normal levels by dietary cholestyramine and mevinolin and decreased about fourfold compared with normal levels by cholesterol feeding or administration of mevalonate. Similar changes in the mRNA levels of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and HMG-CoA synthase were observed under the various conditions. In vitro translation of either CR39 hybrid selected RNA or 1.2-kb CR39 RNA generated by an SP6 in vitro transcription system produced a polypeptide of 39,000 daltons. As deduced from the nucleotide sequence of a full-length CR39 cDNA, the rat CR39 polypeptide contained 344 amino acids and had a molecular weight of 39,615. The predicted amino acid composition and submit molecular weight of the rat CR39 were very similar to those of prenyltransferases isolated from chicken, pig, and human. The sequence of amino acid residues 173 through 203 in the rat CR39 polypeptide showed that 17 out of 30 matched an active-site peptide of avian liver prenyltransferase. Thus, alterations in the rate of cholesterogenesis resulted in the coordinate regulation of three mRNAs encoding HMG-CoA reductase, HMG-CoA synthase, and CR39, the latter being tentatively identified as prenyltransferase.

Regulation of rat liver 3-hydroxy-3-methylglutaryl coenzyme A synthase and the chromosomal localization of the human gene

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase was purified to homogeneity from rat liver cytoplasm. The active enzyme is a dimer composed of identical subunits of Mr = 53,000. The amino acid composition and the NH2-terminal sequence are presented. Partial cDNA clones for the enzyme were isolated by screening of a rat liver lambda gt11 expression library with antibodies raised against the purified protein. The identity of the clones was confirmed by hybrid selection and translation. When rats were fed diets supplemented with cholesterol, cholestyramine, or cholestyramine plus mevinolin, the hepatic protein mass of cytoplasmic synthase, as determined by immunoblotting, was 25, 160, and 1100%, respectively, of the mass observed in rats fed normal chow. Comparable changes in enzyme activity were observed. Approximately 9-fold increases in both HMG-CoA synthase mRNA mass and synthase mRNA activity were observed when control diets were supplemented with cholestyramine and mevinolin. When rats were fed these two drugs and then given mevalonolactone by stomach intubation, there was a 5-fold decrease of synthase mRNA within 3 h. These results indicate that cytoplasmic synthase regulation occurs primarily at the level of mRNA. This regulation is rapid and coordinate with that observed for HMG-CoA reductase. The chromosomal localization of human HMG-CoA synthase was determined by examining a panel of human-mouse somatic cell hybrids with the rat cDNA probe. Interestingly, the synthase gene resides on human chromosome 5, which has previously been shown to contain the gene for HMG-CoA reductase. Regional mapping, performed by examination of a series of chromosome 5 deletion mutants and by in situ hybridization to human chromosomes indicates that the two genes are not tightly clustered.

Transcriptional regulation of the 3-hydroxy-3-methylglutaryl coenzyme A reductase gene in rat liver

This study addresses whether transcriptional control of the 3-hydroxy-3-methylglutaryl coenzyme A reductase gene in rat liver plays a role in determining the level of reductase mRNA. Isolated rat liver nuclei were allowed to elongate nascent RNA transcripts in the presence of [alpha-32P]CTP, and radiolabeled nuclear reductase RNA was quantitated by filter hybridization. Rats fed a diet supplemented with the drugs cholestyramine and mevinolin and having 20-60-fold induced levels of reductase mRNA exhibited levels of reductase transcription which were 20-fold higher than in rats fed an unsupplemented diet. Over 90% of the transcription of the reductase gene was inhibited by concentrations of alpha-amanitin which selectively inhibit RNA polymerase II. Administration of mevalonolactone (the end product of the reaction catalyzed by reductase) to rats fed cholestyramine and mevinolin caused an 80% decrease in the rate of reductase transcription by approximately 1 h. We conclude that under these conditions changes in reductase transcription are primarily responsible for the regulation of reductase mRNA levels.

Role of mevalonate in regulation of cholesterol synthesis and 3-hydroxy-3-methylglutaryl coenzyme A reductase in cultured cells and their cytoplasts

H4-II-E-C3 hepatoma cells in culture respond to lipid-depleted media and to mevinolin with increased sterol synthesis from [14C]acetate and rise of 3-hydroxy-3-methylglutaryl coenzyme A reductase levels. Mevalonate at 4 mM concentration represses sterol synthesis and the reductase, and completely abolishes the effects of mevinolin. Mevalonate has little or no effect on sterol synthesis or reductase in enucleated hepatoma cells (cytoplasts) or on reductase in cytoplasts of cultured Chinese hamster ovary (CHO) cells. The sterol-synthesizing system of hepatoma cell cytoplasts and the reductase in the cytoplasts of CHO cells were completely stable for at least 4 hr. While reductase levels and sterol synthesis from acetate followed parallel courses, the effects on sterol synthesis--both increases and decreases--exceeded those on reductase. In vitro translation of hepatoma cell poly(A)+RNAs under various culture conditions gave an immunoprecipitable polypeptide with a mass of 97,000 daltons. The poly(A)+RNA from cells exposed for 24 hr to lipid-depleted media plus mevinolin (1 microgram/ml) contained 2.8 to 3.6 times more reductase-specific mRNA than that of cells kept in full-growth medium, or cells exposed to lipid-depleted media plus mevinolin plus mevalonate. Northern blot hybridization of H4 cell poly(A)+RNAs with [32P]cDNA to the reductase of CHO cells gave two 32P-labeled bands of 4.6 and 4.2 K-bases of relative intensities 1.0, 0.61-1.1, 2.56, and 1.79 from cells kept, respectively, in full-growth medium, lipid-depleted medium plus mevinolin plus mevalonate, lipid-depleted medium plus mevinolin, and lipid-depleted medium. These values approximate the reductase levels of these cells. We conclude that mevalonate suppresses cholesterol biosynthesis in part by being a source of a product that decreases the level of reductase-specific mRNA.

Diurnal rhythm of rat liver mRNAs encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase. Correlation of functional and total mRNA levels with enzyme activity and protein

Rat liver 3-hydroxy-3-methylglutaryl coenzyme A reductase exhibits a diurnal rhythm of activity which coincides with a diurnal rhythm of reductase protein and reductase mRNA levels. This diurnal rhythm of reductase activity, polypeptide mass, and mRNA exists in rats fed a normal diet (unsupplemented rat chow) and in rats fed a diet supplemented with cholestyramine plus or minus mevinolin. Levels of reductase protein were determined by 8 M urea/sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. Reductase mRNA was measured by in vitro translation or blot hybridization of liver RNA. Functional reductase mRNA levels in rats fed a normal diet were approximately 10-fold higher during the middle of the dark cycle than during the middle of the light cycle. Maximum induction of functional reductase mRNA was observed in rats fed cholestyramine and mevinolin. This latter level was 157-fold higher than the level measured at the diurnal low point in rats fed a normal diet. Blot hybridization of liver RNA showed two predominant mRNAs of 4.6 and 4.2 kilobase pairs and a minor species at 6.9 kilobase pairs. These mRNAs exhibited a diurnal rhythm for rats on all three diets and reached peak levels during the 12-h dark period. These data indicate that the diurnal rhythm of reductase mass and activity is closely paralleled by the level of its mRNA.

Regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase mRNA levels in rat liver

Addition of cholestyramine or cholestyramine plus mevinolin to the diet has been reported to increase the activity and mass of rat liver 3-hydroxy-3-methylglutaryl-CoA reductase. The present data show that these same dietary manipulations cause an induction of functional reductase mRNA. RNA was isolated from rat livers and added to an in vitro translation system, and the reductase was immunoprecipitated and analyzed by polyacrylamide gel electrophoresis under denaturing conditions. One protein was specifically immunoprecipitated and was found to have a Mr of 90,000 on 0.5 M urea/sodium dodecyl sulfate/polyacrylamide gels and a Mr of 94,000 on 8 M urea/sodium dodecyl sulfate/polyacrylamide gels. In animals fed rat chow supplemented with 5% cholestyramine and 0.1% mevinolin, reductase mRNA levels were 5.7-fold higher than in animals fed rat chow with 5% cholestyramine and were 16-fold higher than in animals fed rat chow with 5% cholestyramine and given mevalonolactone by stomach intubation. RNA isolated from animals fed a normal diet and killed at the nadir of the diurnal cycle of enzyme activity contained no detectable amounts of reductase mRNA as determined by this assay.