An inducible CRISPR interference library for genetic interrogation of Saccharomyces cerevisiae biology

Genome-scale CRISPR interference (CRISPRi) is widely utilized to study cellular processes in a variety of organisms. Despite the dominance of Saccharomyces cerevisiae as a model eukaryote, an inducible genome-wide CRISPRi library in yeast has not yet been presented. Here, we present a genome-wide, inducible CRISPRi library, based on spacer design rules optimized for S. cerevisiae. We have validated this library for genome-wide interrogation of gene function across a variety of applications, including accurate discovery of haploinsufficient genes and identification of enzymatic and regulatory genes involved in adenine and arginine biosynthesis. The comprehensive nature of the library also revealed refined spacer design parameters for transcriptional repression, including location, nucleosome occupancy and nucleotide features. CRISPRi screens using this library can identify genes and pathways with high precision and a low false discovery rate across a variety of experimental conditions, enabling rapid and reliable assessment of genetic function and interactions in S. cerevisiae.

Phylogenetic debugging of a complete human biosynthetic pathway transplanted into yeast

Cross-species pathway transplantation enables insight into a biological process not possible through traditional approaches. We replaced the enzymes catalyzing the entire Saccharomyces cerevisiae adenine de novo biosynthesis pathway with the human pathway. While the 'humanized' yeast grew in the absence of adenine, it did so poorly. Dissection of the phenotype revealed that PPAT, the human ortholog of ADE4, showed only partial function whereas all other genes complemented fully. Suppressor analysis revealed other pathways that play a role in adenine de-novo pathway regulation. Phylogenetic analysis pointed to adaptations of enzyme regulation to endogenous metabolite level 'setpoints' in diverse organisms. Using DNA shuffling, we isolated specific amino acids combinations that stabilize the human protein in yeast. Thus, using adenine de novo biosynthesis as a proof of concept, we suggest that the engineering methods used in this study as well as the debugging strategies can be utilized to transplant metabolic pathway from any origin into yeast.

C-C bond forming radical SAM enzymes involved in the construction of carbon skeletons of cofactors and natural products

Covering: up to the end of 2017 C-C bond formations are frequently the key steps in cofactor and natural product biosynthesis. Historically, C-C bond formations were thought to proceed by two electron mechanisms, represented by Claisen condensation in fatty acids and polyketide biosynthesis. These types of mechanisms require activated substrates to create a nucleophile and an electrophile. More recently, increasing number of C-C bond formations catalyzed by radical SAM enzymes are being identified. These free radical mediated reactions can proceed between almost any sp3 and sp2 carbon centers, allowing introduction of C-C bonds at unconventional positions in metabolites. Therefore, free radical mediated C-C bond formations are frequently found in the construction of structurally unique and complex metabolites. This review discusses our current understanding of the functions and mechanisms of C-C bond forming radical SAM enzymes and highlights their important roles in the biosynthesis of structurally complex, naturally occurring organic molecules. Mechanistic consideration of C-C bond formation by radical SAM enzymes identifies the significance of three key mechanistic factors: radical initiation, acceptor substrate activation and radical quenching. Understanding the functions and mechanisms of these characteristic enzymes will be important not only in promoting our understanding of radical SAM enzymes, but also for understanding natural product and cofactor biosynthesis.

Translational regulation by miR-301b upregulates AMP deaminase in diabetic hearts

AMP deaminase (AMPD) plays a crucial role in adenine nucleotide metabolism. Recently we found that upregulated AMPD activity is associated with ATP depletion and contractile dysfunction under the condition of pressure overloading in the heart of a rat model of type 2 diabetes mellitus (T2DM), OLETF. Here we examined the mechanism of AMPD upregulation by T2DM. The protein level of 90-kDa full-length AMPD3 was increased in whole myocardial lysates by 55% in OLETF compared to those in LETO, a non-diabetic control. In contrast, the mRNA levels of AMPD3 in the myocardium were similar in OLETF and LETO. AMPD3 was comparably ubiquitinated in OLETF and LETO, and its degradation ex vivo was more sensitive to MG-132, a proteasome inhibitor, in OLETF than in LETO. MicroRNA array analysis revealed downregulation (>50%) of 57 microRNAs in OLETF compared to those in LETO, among which miR-301b was predicted to interact with the 3'UTR of AMPD3 mRNA. AMPD3 protein level was significantly increased by a miR-301b inhibitor and was decreased by a miR-301b mimetic in H9c2 cells. A luciferase reporter assay confirmed binding of miR-301b to the 3'UTR of AMPD3 mRNA. Transfection of neonatal rat cardiomyocytes with a miR-301b inhibitor increased 90-kDa AMPD3 and reduced ATP level. The results indicate that translational regulation by miR-301b mediates upregulated expression of cardiac AMPD3 protein in OLETF, which potentially reduces the adenine nucleotide pool at the time of increased work load. The miR-301b-AMPD3 axis may be a novel therapeutic target for intervening enegy metabolism in diabetic hearts.

Involvement of Gαs-proteins in the action of relaxin-like gonad-stimulating substance on starfish ovarian follicle cells

Gonad-stimulating substance (GSS) in starfish is the only known invertebrate peptide hormone responsible for final gamete maturation, rendering it functionally analogous to gonadotropins in vertebrates. In breeding season (stage V), GSS stimulates oocyte maturation to induce 1-methyladenine (1-MeAde) by ovarian follicle cells. The hormonal action of GSS is mediated through the activation of its receptor, G-proteins and adenylyl cyclase. It has been reported that GSS fails to induce 1-MeAde and cyclic AMP (cAMP) production in follicle cells of ovaries during oogenesis (stage IV). This study examined the regulatory mechanism how ovarian follicle cells acquire the potential to respond to GSS by producing 1-MeAde and cAMP. Because the failure of GSS action was due to G-proteins of follicle cells, the molecular structures of Gαs, Gαi, Gαq and Gβ were identified in follicle cells of starfish Asterina pectinifera. The cDNA sequences of Gαs, Gαi, Gαq and Gβ consisted of ORFs encoding 379, 354, 353 and 353 amino acids. The expression levels of Gαs were extremely low in follicle cells at stage IV, whereas the mRNA levels increased markedly in stage V. On contrary, the mRNA levels of Gαi were almost constant regardless of stage IV and V. These findings strongly suggest that de novo synthesis of Gαs-proteins is contributed to the action of GSS on follicle cells to produce 1-MeAde and cAMP.

A fundamental regulatory role of formate on thuringiensin production by resting cell of Bacillus thuringiensis YBT-032

In this work, a fundamental regulatory role of formate on thuringiensin production by resting cell of Bacillus thuringiensis YBT-032 was investigated. Nicotinamide adenine dinucleotide (NADH) production and formate dehydrogenase activity increased with formate addition from 0.5 to 2.0 g/L, respectively. However, with the formate addition of 1.5 g/L, the activities of pyruvate kinase and glucose 6-phosphate dehydrogenase reached a peak and increased by 316 and 150% relative to those of the control, respectively. In addition, intracellular production of pyruvate, aspartate, citrate and adenine were significantly enhanced by 75, 66, 32 and 78% as well. An improvement (90%) of thuringiensin production was also successfully obtained. Interestingly to point out, thuringiensin yield was closely correlative with adenine production, and the linear relationship was also observed. The results suggest that appropriate formate addition did act as a modulator and facilitate carbon flux in glycolysis and pentose phosphate pathway to synthesize adenine and thuringiensin via intracellular NADH availability.

From genes to proteins to behavior: a laboratory project that enhances student understanding in cell and molecular biology

In the laboratory, students can actively explore concepts and experience the nature of scientific research. We have devised a 5-wk laboratory project in our introductory college biology course whose aim was to improve understanding in five major concepts that are central to basic cellular, molecular biology, and genetics while teaching molecular biology techniques. The project was focused on the production of adenine in Saccharomyces cerevisiae and investigated the nature of mutant red colonies of this yeast. Students created red mutants from a wild-type strain, amplified the two genes capable of giving rise to the red phenotype, and then analyzed the nucleotide sequences. A quiz assessing student understanding in the five areas was given at the start and the end of the course. Analysis of the quiz showed significant improvement in each of the areas. These areas were taught in the laboratory and the classroom; therefore, students were surveyed to determine whether the laboratory played a role in their improved understanding of the five areas. Student survey data demonstrated that the laboratory did have an important role in their learning of the concepts. This project simulated steps in a research project and could be adapted for an advanced course in genetics.

Production of the bioactive compound eritadenine by submerged cultivation of shiitake (Lentinus edodes) mycelia

Fruit bodies and mycelia of shiitake mushroom ( Lentinus edodes) have been shown to contain the cholesterol-reducing compound eritadenine, 2( R),3( R)-dihydroxy-4-(9-adenyl)butyric acid. In the search for a production method for eritadenine, shiitake mycelia were investigated in the present study. The mycelia were cultivated both in shake flasks and in bioreactors, to investigate the effects of pH, stirring rate, and reactor type on the production and distribution of eritadenine. Both the biomass and the culture broth were examined for their eritadenine content. In the shake flasks, the final concentration of eritadenine was 1.76 mg/L and eritadenine was equally distributed between the mycelia and the growth media. In the bioreactors, the shiitake mycelia were found to contain eritadenine in relatively low levels, whereas the majority, 90.6-98.9%, was detected in the growth media. Applying a stirring rate of 250 rpm during bioreactor cultivation resulted in the highest eritadenine concentrations: 10.23 mg/L when the pH was uncontrolled and 9.59 mg/L when the pH was controlled at 5.7. Reducing the stirring rate to 50 rpm resulted in a decreased eritadenine concentration, both at pH 5.7 (5.25 mg/L) and when pH was not controlled (5.50 mg/L). The mycelia in the shake flask cultures appeared as macroscopic aggregates, whereas mycelia cultivated in bioreactors grew more as freely dispersed filaments. This study demonstrates for the first time the extra- and intracellular distribution of eritadenine produced by shiitake mycelial culture and the influence of reactor conditions on the mycelial morphology and eritadenine concentrations.

A polymorphism in CD14 modifies the effect of farm milk consumption on allergic diseases and CD14 gene expression

BACKGROUND

Consumption of farm milk in early life is associated with less asthma and allergies.

OBJECTIVE

We hypothesized that genetic variation in the innate immunity receptor CD14 might modify the association between farm milk consumption and asthma and atopy.

METHODS

Questionnaire data, serum IgE levels, and genotypes for 4 single nucleotide polymorphisms in CD14 were assessed in farmers' and nonfarmers' children from 2 European populations (Allergy and Endotoxin study, n = 576; Prevention of Allergy Risk factors for Sensitization in children related to Farming and Anthroposophic Lifestyle study, n = 1539). In a subsample (n = 222) CD14 gene expression was measured in peripheral blood leukocytes. The effects of farm milk and CD14 genotypes on asthma, allergies, and CD14 expression and their interactions were investigated.

RESULTS

We found a significant interaction between genetic variation in CD14/-1721 and farm milk consumption. Adjusted odds ratios for the association between farm milk and asthma varied between the genotypes: AA, 0.18 (95% CI, 0.07-0.47); AG, 0.47 (95% CI, 0.26-0.86); and GG, 0.98 (95% CI, 0.46-2.08). Similar patterns were observed for symptoms of allergic rhinoconjunctivitis and pollen sensitization. CD14/-1721 also modified the association between farm milk and CD14 gene expression (adjusted geometric means ratios: AA, 1.61 (95% CI, 0.98-2.66); AG, 1.11 (95% CI, 0.71-1.72); and GG, 0.76 (95% CI, 0.39-1.48).

CONCLUSION

The protective effect of farm milk consumption on allergic diseases is stronger in children carrying the A allele in CD14/-1721 than in children homozygous for the G allele. This might be mediated through farm milk-induced upregulated CD14 gene expression.

CLINICAL IMPLICATIONS

Our results support the hypothesis that the inverse association between farm milk consumption and allergic diseases is mediated by CD14-activated innate immune mechanisms.

Immobilized Escherichia coli BL21 as a catalyst for the synthesis of adenine and hypoxanthine nucleosides

Different supports, such as alginate, agar, agarose, and polyacrylamide, were used to immobilize Escherichia coli BL 21 by entrapment techniques. The transglycosylation reaction involved in the synthesis of adenosine from uridine and adenine was chosen as a model system to study the characteristics of these biocatalysts. Whole cells immobilized on agarose proved to be optimal and could be used up to 30 times without significant loss of activity. This biocatalyst was further employed to test its ability in the synthesis of other adenine and hypoxanthine nucleosides. Ribo-, 2'-deoxyribo-, and arabinonucleosides could be prepared in high yields starting from the corresponding pyrimidine nucleosides and purine bases. Similar product yields were obtained with both free and immobilized cells, though, in the latter case, a longer reaction time was necessary.

Regulation of purine nucleotide biosynthesis: in yeast and beyond

Purine nucleotides are critically important for the normal functioning of cells due to their myriad of activities. It is important for cells to maintain a balance in the pool sizes of the adenine-containing and guanine-containing nucleotides, which occurs by a combination of de novo synthesis and salvage pathways that interconvert the purine nucleotides. This review describes the mechanism for regulation of the biosynthetic genes in the yeast Saccharomyces cerevisiae and compares this mechanism with that described in several microbial species.

A survey of all 11 ABC transporters in fission yeast: two novel ABC transporters are required for red pigment accumulation in a Schizosaccharomyces pombe adenine biosynthetic mutant

ATP-binding cassette (ABC) proteins transport a wide variety of substrates, including sugars, amino acids, metal ions, lipids, peptides and proteins, across membranes, and most ABC proteins contain transmembrane domains (ABC transporters). Sequencing of theSchizosaccharomyces pombegenome has allowed identification of all genes encoding ABC transporters in fission yeast. To date, six such genes have been characterized, and an additional five genes encoding ABC transporters were identified from the genome sequence. In an attempt to characterize all of the ABC transporters in fission yeast, all 11 genes were disrupted. While all the genes were found to be dispensable for cell viability, some disruptants lacked apparent phenotypes. GFP-tagged ABC transporters were localized to membranes as follows: plasma membrane (2), vacuolar membrane (4), mitochondrial membrane (2), endoplasmic reticulum membrane (2), and endosome and Golgi membranes (1). Two Cluster II. 1 proteins, Abc2p (SPAC3F10.11c) and Abc4p (SPAC30.04c), were found to be localized to vacuolar membranes, and to be responsible for accumulation of a characteristic red pigment in the vacuole of an adenine biosynthetic mutant. The doubly disrupted mutantabc2Δabc4Δ exhibited drug sensitivity, and a decreased accumulation of monochlorobimane, suggesting that both of the proteins encoded by these genes are involved in detoxification of xenobiotics, and vacuolar sequestration of glutathioneS-conjugates.

Adenine auxotrophic mutants of Aspergillus oryzae: development of a novel transformation system with triple auxotrophic hosts

adeA and adeB genes homologous to Saccharomyces cerevisiae ADE1 and ADE2, respectively, were cloned from Aspergillus oryzae. AdeA and AdeB share 62.8% and 52.5% identities with S. cerevisiae Ade1 and Ade2, respectively. In order to obtain triple auxotrophic mutants from A. oryzae, 12 red-colored mutant colonies were isolated by UV mutagenesis of a double auxotrophic host, NS4 (niaD(-), sC(-)), as a parent strain. All the mutants exhibited adenine auxotrophy and showed fluorescence in the vacuoles due to accumulation of a purine biosynthetic pathway precursor. Adenine auxotrophy of all the mutants was restored by introduction of either A. oryzae adeA or adeB genes. Sequence analysis demonstrated that substitutions or deletions of a single base pair occurred, inducing substitutions or frame shifts of amino acid sequences in both ade genes complementing the mutants. This study provides a novel host-vector system with triple auxotrophy in A. oryzae.

Genetic determination of ploidy level in Xanthophyllomyces dendrorhous

Xanthophyllomyces dendrorhous (formely Phaffia rhodozyma) is a basidiomycetous yeast-like fungus that produces carotenoids useful for the food industry. Recently, its sexual cycle was reported but little is known about its genetic constitution. To inquire into the ploidy state of X. dendrorhous, biased mutant spectrum, genetic complementation and mitotic recombination analysis were used. A wild-type strain was subjected to N-methyl-N'-nitro-N-nitrosoguanidine mutagenic treatment. Auxotrophic and carotene mutants were forced to revert to the wild-type phenotype. Pigment producing and prototroph revertants behaved as diploid except for adenine less mutants. These results are in agreement with the limited spectrum of auxotrophs obtained in this strain for the ADE1 locus. To analyze the genetic characteristic of the adenine genetic marker of X. dendrorhous, protoplast fusion experiments with several adenine less mutants were performed. The experiments presented in this work suggest that the ATCC 2430 (UDC 67-385) strain of X. dendrorhous is diploid and a heterozygous constitution is proposed for the ADE1 locus.

Detection and quantification of 1,N6-ethenoadenine in human urine by stable isotope dilution capillary gas chromatography/negative ion chemical ionization/mass spectrometry

1,N(6)-Ethenoadenine (epsilonAde) is a promutagenic lesion detected in tissue DNA; it has been shown that epsilonAde can be repaired by human DNA glycosylases, and it is expected to be excreted in urine. In this paper, we present for the first time detection and accurate quantification of epsilonAde in human urine samples by a highly sensitive and specific stable isotope dilution gas chromatography/negative ion chemical ionization/mass spectrometric assay (GC/NICI/MS). Analysis by GC/NICI/MS includes adduct enrichment by a solid phase extraction column, followed by electrophore labeling and postderivatization cleanup. Using selective ion monitoring mode, the assay allows quantification of 0.5 pg of epsilonAde in as little as 0.1 mL of the urine sample, which is equivalent to corresponding concentration quantification limit of 31 pM. Using this assay, concentrations of epsilonAde in the 24 h urine samples of 23 healthy individuals were determined, which ranged from 0 to 124 pg/mL. After we adjusted for creatinine, a statistically significant correlation was found between epsilonAde excretion and cigarette smoking in males (p = 0.03). Thus, this stable isotope dilution GC/NICI/MS assay offers a sensitive and accurate quantification of urinary epsilonAde as a potential biomarker for oxidative damage of DNA and repair.

Role of etheno DNA adducts in carcinogenesis induced by vinyl chloride in rats

Vinyl chloride, a hepatocarcinogen in humans and rodents, can form promutagenic etheno bases in DNA after metabolic activation. The formation of 1,N6-ethenoadenine (epsilon A) and 3,N4-ethenocytosine (epsilon C) was measured in adult Sprague-Dawley rats by immunoaffinity purification and 32P-postlabelling. A highly variable background was found in all tissues from untreated animals: the mean molar ratios of epsilon A:A and epsilon C:C in DNA ranged from 0.043 x 10(-8) to 31.2 x 10(-8) and from 0.062 x 10(-8) to 20.4 x 10(-8), respectively. After exposure to 500 ppm vinyl chloride by inhalation (4 h/day, 5 days/week for 8 weeks), increased levels of epsilon A were found in the liver, lung, circulating lymphocytes and testis, the mean (+/- SD) of induced levels (treated-control values) being (4.1 +/- 1.5) x 10(-8) for these tissues. No increase in the epsilon A:A ratio was observed in kidney, brain or spleen. The levels of epsilon C increased in all the tissues examined except the brain. The mean value of the induced epsilon C:C ratios was (7.8 +/- 1.2) x 10(-8) for the liver, kidney, lymphocytes and spleen, and these ratios were higher in the lung (28 x 10(-8)) and testis (19 x 10(-8)). The results suggest a variable repair capacity for epsilon A or epsilon C in different tissues. The results are discussed in relation to published studies on the accumulation and persistence of etheno bases in the liver during and after exposure to vinyl chloride and on mutation spectra in the ras and p53 genes in liver tumours induced by vinyl chloride. In addition, we show that the linear relationship established for monofunctional alkylating agents between their carcinogenic potency in rodents and their covalent binding index for promutagenic bases in hepatic DNA holds for vinyl chloride. It is concluded that etheno bases are critical lesions in hepatocarcinogenesis induced by vinyl chloride. For a better understanding of the mechanism of action of this compound, further work is needed on the role of DNA repair pathways and of endogenous lipid peroxidation products in the formation and persistence of etheno bases in vivo.

Development of a whole cell assay to measure methotrexate-induced inhibition of thymidylate synthase and de novo purine synthesis in leukaemia cells

The cellular pharmacology of methotrexate (MTX) is complex, involving the inhibition of both de novo thymidylate and purine biosynthesis. Measurement of MTX-induced inhibition of de novo thymidylate and purine biosynthesis may allow optimisation of MTX therapy, and the aim of this study was to develop an assay to measure the activity of both pathways in the same cell sample, and so determine the effects of MTX treatment. In situ thymidylate synthase (EC 2.1.1.45) activity was measured by the release of 3H2O from [5'-3H]deoxyuridine and de novo purine synthesis by the incorporation of [14C]formate into adenine and guanine. Incubation of human leukaemia CCRF-CEM cells for 22 hr with 50 nM MTX resulted in approximately 90% inhibition of in situ thymidylate synthase activity, relative to control untreated cells, and after exposure to 1000 nM MTX activity could not be detected. In contrast, de novo purine synthesis, measured in the same sample, was not inhibited by exposure to 50 nM MTX, although activity was again completely abolished by exposure to 1000 nM MTX. To demonstrate the utility of the assay, lymphoblasts isolated from a child with acute lymphoblastic leukaemia (ALL) were also incubated for 22 hr with 1000 nM MTX. Both in situ thymidylate synthase activity and de novo purine synthesis were significantly inhibited, by 70% and 60% respectively, relative to the activity in untreated cells.

Methyl donor for 1-methyladenine biosynthesis in starfish ovarian follicle cells

1-Methyladenine (1-MeAde), the oocyte maturation-inducing substance of starfish, is produced by ovarian follicle cells upon stimulation with a gonad-stimulating substance (GSS) released from radial nerves. It has been reported that a process of methylation is involved in GSS-induced 1-MeAde production by starfish ovarian follicle cells. The present study sought to identify a possible methyl donor for 1-MeAde biosynthesis in follicle cells of the starfish Asterina pectinifera. When isolated follicle cells were incubated with [methyl-(14)C]methionine (Met), there was an increase in the level of radiolabeled S-adenosylmethionine (SAM). After further incubation with GSS, the [methyl-(14)C]SAM level decreased, concomitant with a marked increase in radiolabeled 1-MeAde production. The amount of [methyl-(14)C]SAM consumed under the influence of GSS was similar to the amount of [methyl-(14)C]1-MeAde produced. Therefore, it is concluded that SAM is a methyl donor for 1-MeAde biosynthesis in starfish ovarian follicle cells. On the other hand, it is likely that the purine molecule of 1-MeAde is not derived from SAM but from ATP. 3-Isobutyl-1-methylxanthine, a potent inhibitor of cyclic AMP phosphodiesterase, also caused a reduction in the level of radiolabeled SAM following 1-MeAde production. This suggests that the methylation process of 1-MeAde biosynthesis in starfish ovarian follicle cells upon stimulation with GSS is mediated by a second messenger, cyclic AMP.

1-Methyladenine production from ATP by starfish ovarian follicle cells

1-Methyladenine (1-MeAde), the oocyte maturation-inducing substance in starfish, is produced by ovarian follicle cells upon stimulation with a gonad-stimulating substance (GSS) released from the radial nerves. We have shown previously that GSS causes a reduction in the intracellular levels of ATP coincident with 1-MeAde production. The present study examined whether the adenine molecule of 1-MeAde is directly derived from ATP. When isolated follicle cells from the starfish Asterina pectinifera were preloaded with [U-14C]adenine or [U-14C]adenosine, there was an increase in the intracellular levels of radiolabeled adenine nucleotides, particularly ATP. Following further incubation with GSS, the intracellular levels of radiolabeled ATP decreased, concomitant with a marked increase in the levels of [14C]1-MeAde in the medium. The amount of ATP consumed under the influence of GSS was similar to the amount of 1-MeAde produced. However, there was no change in the levels of ADP and AMP regardless of the presence or absence of GSS. These findings strongly suggest that 1-MeAde is synthesized from ATP as a substrate in follicle cells under the influence of GSS. Furthermore, using [methyl-3H]methionine, the methyl group of 1-MeAde was found to be derived from methionine. Thus GSS appears to stimulate the synthesis of 1-MeAde from ATP via the methylation process in starfish ovarian follicle cells.

The prebiotic synthesis of modified purines and their potential role in the RNA world

Modified purines are found in all organisms in the tRNA, rRNA, and even DNA, raising the possibility of an early role for these compounds in the evolution of life. These include N6-methyladenine, 1-methyladenine, N6,N6-dimethyladenine, 1-methylhypoxanthine, 1-methylguanine, and N2-methylguanine. We find that these bases as well as a number of nonbiological modified purines can be synthesized from adenine and guanine by the simple reaction of an amine or an amino group with adenine and guanine under the concentrated conditions of the drying-lagoon or drying-beach model of prebiotic synthesis with yields as high as 50%. These compounds are therefore as prebiotic as adenine and guanine and could have played an important role in the RNA world by providing additional functional groups in ribozymes, especially for the construction of hydrophobic binding pockets.

Cloning of oxetanocin A biosynthetic and resistance genes that reside on a plasmid of Bacillus megaterium strain NK84-0128

Bacillus megaterium strain NK84-0218 produces a potent antiviral antibiotic, oxetanocin A, which has an oxetanosyl-N-glycoside linkage to an adenine moiety. However, the oxetanocin A productivity of the original strain was unstable and low. In this study, oxetanocin A productivity and resistance was shown to be lost simultaneously when a 51.5-kb plasmid, pOXT1, was cured during cultivation. The deficiency of oxetanocin A productivity and resistance was restored by re-introduction of the pOXT1 plasmid into the cured strain. By a cloning experiment it was shown that a 6.8-kb BglI-D fragment of the pOXT1 plasmid was responsible for oxetanocin A productivity and resistance.

Mutations in the yeast Myb-like protein Bas1p resulting in discrimination between promoters in vivo but notin vitro

Bas1p is a yeast transcription factor that activates expression of purine and histidine biosynthesis genes in response to extracellular purine limitation. The N-terminal part of Bas1p contains an Myb-like DNA binding domain composed of three tryptophan-rich imperfect repeats. We show that mutating the conserved tryptophan residues in the DNA binding domain of Bas1p severely impairs in vivo activation of target genes and in vitro DNA binding of Bas1p. We also found that two mutations (H34L and W42A) in the first repeat make Bas1p discriminate between promoters in vivo . These two BAS1 mutants are able to activate expression of an HIS4-lacZ fusion but not that of ADE1-lacZ or ADE17-lacZ fusions. Surprisingly, these mutant proteins bind equally well to the three promoters in vitro , suggesting that the mutations affect the interaction of Bas1p with some promoter-specific factor(s) in vivo . By mutating a potential nucleotide binding site in the DNA binding domain of Bas1p, we also show that this motif does not play a major role in purine regulation of Bas1p activity. Finally, using a green fluorescence protein (GFP)-Bas1p fusion, we establish the strict nuclear localization of Bas1p and show that it is not affected by extracellular adenine.

The isolation and characterization of Saccharomyces cerevisiae mutants that constitutively express purine biosynthetic genes

In response to an external source of adenine, yeast cells repress the expression of purine biosynthesis pathway genes. To identify necessary components of this signalling mechanism, we have isolated mutants that are constitutively active for expression. These mutants were named bra (for bypass of repression by adenine). BRA7 is allelic to FCY2, the gene encoding the purine cytosine permease and BRA9 is ADE12, the gene encoding adenylosuccinate synthetase. BRA6 and BRA1 are new genes encoding, respectively, hypoxanthine guanine phosphoribosyl transferase and adenylosuccinate lyase. These results indicate that uptake and salvage of adenine are important steps in regulating expression of purine biosynthetic genes. We have also shown that two other salvage enzymes, adenine phosphoribosyl transferase and adenine deaminase, are involved in activating the pathway. Finally, using mutant strains affected in AMP kinase or ribonucleotide reductase activities, we have shown that AMP needs to be phosphorylated to ADP to exert its regulatory role while reduction of ADP into dADP by ribonucleotide reductase is not required for adenine repression. Together these data suggest that ADP or a derivative of ADP is the effector molecule in the signal transduction pathway.

Evidence that complex formation by Bas1p and Bas2p (Pho2p) unmasks the activation function of Bas1p in an adenine-repressible step of ADE gene transcription

Bas1p and Bas2p (Pho2p) are Myb-related and homeodomain DNA binding proteins, respectively, required for transcription of adenine biosynthetic genes in Saccharomyces cerevisiae. The repression of ADE genes in adenine-replete cells involves down-regulation of the functions of one or both of these activator proteins. A LexA-Bas2p fusion protein was found to activate transcription from a lexAop-lacZ reporter independently of both BAS1 function and the adenine levels in the medium. In contrast, a LexA-Bas1p fusion activated the lexAop reporter in a BAS2-dependent and adenine-regulated fashion. The DNA binding activity of Bas2p was not needed for its ability to support activation of the lexAop reporter by LexA-Bas1p, indicating that LexA-Bas1p recruits Bas2p to this promoter. The activation functions of both authentic Bas1p and LexA-Bas1p were stimulated under adenine-repressing conditions by overexpression of Bas2p, suggesting that complex formation by these proteins is inhibited in adenine-replete cells. Replacement of Asp-617 with Asn in Bas1p or LexA-Bas1p allowed either protein to activate transcription under repressing conditions in a manner fully dependent on Bas2p, suggesting that this mutation reduces the negative effect of adenine on complex formation by Bas1p and Bas2p. Deletions of N-terminal and C-terminal segments from the Bas1p moiety of LexA-Bas1p allowed high-level activation by the truncated proteins independently of Bas2p and adenine levels in the medium. From these results we propose that complex formation between Bas1p and Bas2p unmasks a latent activation function in Bas1p as a critical adenine-regulated step in transcription of the ADE genes.

apd1+, a gene required for red pigment formation in ade6 mutants of Schizosaccharomyces pombe, encodes an enzyme required for glutathione biosynthesis: a role for glutathione and a glutathione-conjugate pump

Mutants in the adenine biosynthetic pathway of yeasts (ade1 and ade2 of Saccharomyces cerevisiae, ade6 and ade7 of Schizosaccharomyces pombe) accumulate an intense red pigment in their vacuoles when grown under adenine-limiting conditions. The precise events that determine the formation of the pigment are however, still unknown. We have begun a genetic investigation into the nature and cause of pigmentation of ade6 mutants of S. pombe and have discovered that one of these pigmentation defective mutants, apd1 (adenine pigmentation defective), is a strict glutathione auxotroph. The gene apd1+ was found to encode the first enzyme in glutathione biosynthesis, gamma-glutamylcysteine synthetase, gcs1+. This gene when expressed in the mutant could confer both glutathione prototrophy and the characteristic red pigmentation, and disruption of the gene led to a loss in both phenotypes. Supplementation of glutathione in the medium, however, could only restore growth but not the pigmentation because the cells were unable to achieve sufficient intracellular levels of glutathione. Disruption of the second enzyme in glutathione biosynthesis, glutathione synthetase gsh2+, also led to glutathione auxotrophy, but only a partial defect in pigment formation. A reevaluation of the major amino acids previously reported to be present in the pigment indicated that the pigment is probably a glutathione conjugate. The ability of vanadate to inhibit pigment formation indicated that the conjugate was transported into the vacuole through a glutathione-conjugate pump. This was further confirmed using strains of S. cerevisiae bearing disruptions in the recently identified glutathione-conjugate pump, YCF1, where a significant reduction in pigment formation was observed. The pump of S. pombe is distinct from the previously identified vacuolar pump, hmt1p, for transporting cadystin peptides into vacuoles of S. pombe.

The red/white colony color assay in the yeast Saccharomyces cerevisiae: epistatic growth advantage of white ade8-18, ade2 cells over red ade2 cells

In the yeast Saccharomyces cerevisiae the ade2, and/or the ade1, mutation in the adenine biosynthetic pathway leads to the accumulation of a cell-limited red pigment, while epistatic mutations in the same pathway, i.e. ade8, preclude this phenomenon, resulting in normal white colonies. The shift in color from red to white (or vice versa) with a combination of appropriate wild-type and mutant alleles of the adenine-pathway genes has been widely utilized as a non-selective phenotype to visualise and quantify the occurrence of various genetic events such as recombination, conversion and aneuploidy. It has provided an invaluable tool for the study of gene dosage and plasmid stability. In competition experiments between disrupted ade2, ade8-18 transformants carrying either a functional or non-functional episomal ADE8 gene, we verified that white ade8 ade2 cells show a remarkable selective advantage over red ade2 cells, with important implications on the use of this assay for the monitoring of genetic events. The accumulation of the red pigment in ade2 cells is likely to be the cause for impaired growth in these cells.

The in vitro methylation of DNA by a minor groove binding methyl sulfonate ester

The preparation of sequence and groove specific DNA methylating agents based on N-methylpyrrolecarboxamide subunits appended with an O-methyl sulfonate ester functionality (MeOSO2(CH2)2-Lex) has previously been described [Zhang, Y., Chen, F.-X., Mehta, P., and Gold, B. (1993) Biochemistry 32,7954-7965]. In contrast to simple methyl sulfonate esters, e.g., methyl methanesulfonate (MMS), which predominantly methylate at 7-guanine, MeOSO2-(CH2)2-Lex affords N3-methyladenine (3-MeAde) as its major adduct. Using competitive ELISA determinations, the methylation at major and minor groove sites in calf thymus DNA by MeOSO2(CH2)2-Lex has been precisely quantitated. The yields of N7-methylguanine (7-MeGua), 3-MeAde, and O6-methyldeoxyguanosine (6-Me-dGuo) are 0.424, 3.195, and 0.0027 mmol of adduct/mol of DNA, respectively, using 10 microM MeOSO2(CH2)2-Lex and 100 microM DNA. This compares to 0.773, 0.072, and 0.0033 mmol of adduct/mol of DNA for 7-MeGua, 3-MeAde, and 6-Me-dGuo, respectively, using MMS. The increase in the yield of 3-MeAde due to the minor groove equilibrium binding properties of MeOSO2(CH2)2-Lex is approximately 40-fold relative to MMS.

[Transfer of S. typhimurium strains with mutation to a noncultured state, disrupting synthesis of purine bases]

Effects of mutations impairing the synthesis of purine nucleotides on the process of S. typhimurium cells transfer into an unculturable state (US) have been studied. The presence of guaA- mutation in the cells was found to lead to a sooner transfer to US in comparison with the cells of reference strain. The presence of purE- mutation does not tell on the rate of mutant cells transfer in US.

Formation of 1,N6-ethenoadenine and 3,N4-ethenocytosine by lipid peroxidation products and nucleic acid bases

Lipid peroxidation (LPO) products are known to interact with DNA, yielding several types of adduct with nucleobases. In this study, we demonstrate the formation of two ethenobase adducts, 1,N6-ethenoadenine and 3,N4-ethenocytosine, by reaction of LPO products with nucleic acid bases. Rat liver microsomes were incubated at 37 degrees C for 30 min in the presence of inducers of LPO [Fe(II) or cumene hydroperoxide] and adenine or cytosine nucleotides or nucleosides, followed by further heating at 80 degrees C for 30 min to complete the reactions. The etheno adducts detected after immunoaffinity chromatography were 1,N6-etheno-cAMP and 1,N6-etheno-2'-deoxyadenosine (HPLC/fluorimetry), 3,N4-etheno-2'-deoxycytidine (competitive radioimmunoassay), and 1,N6-etheno-2'-deoxyadenosine 3'-monophosphate and 3,N4-etheno-2'-deoxycytidine 3'-monophosphate (32P-postlabeling). Incubation of arachidonic acid supplemented with Fe(II) also led to the formation of the 1,N6-etheno adduct from cAMP. LPO intermediates that may be involved are discussed. These data suggest that etheno adducts may be markers of DNA damage associated with LPO.

The ade6 gene of the fission yeast as a target for antisense and ribozyme RNA-mediated suppression

A genetic system for the analysis of antisense and ribozyme mechanisms is a much needed experimental tool, and yeast represent a favorable organism on which to base such a system. We have shown previously that the fission yeast Schizosaccharomyces pombe has potential to satisfy the requirements of such a system. This report describes experiments designed to determine if antisense and ribozyme RNA-mediated gene suppression will be generally applicable to other genes in S. pombe. Antisense and ribozyme RNAs designed to suppress the ade6 gene were expressed at high levels from episomal expression vectors. The ade6 gene was chosen as a target as mutations within the gene confer adenine auxotrophy and a red colony phenotype, and it was expected that antisense or ribozyme RNA-mediated mutant phenocopies would exhibit the same readily detectable phenotype. No phenotypic indication of ade6 suppression was detected in transformed yeast, and ade6 target mRNA was analyzed by primer extension and Northern analysis. Initially, conflicting results were obtained from these techniques, which were determined to be due to duplex formation between antisense and target RNA in vitro. No detectable reduction in the ade6 mRNA levels was found, and it was concluded that the gene was not suppressed by the antisense or ribozyme RNAs tested. These results confirm that in S. pombe as with other organisms, the susceptibility of genes to RNA-mediated suppression may be gene specific and that design of antisense and ribozyme genes will be an empirical process.

Characterization of BcgI, a new kind of restriction-modification system

The BcgI restriction enzyme from Bacillus coagulans is unusual in that it cleaves on both sides of its recognition site, CGAN6TGC, releasing a fragment that includes the site and several bases on each side. We report the organization and nucleotide sequences of the genes for the BcgI restriction-modification system and the properties of the proteins that they encode. The system comprises two adjacent, similarly oriented genes. The proximal gene, bcgIA, codes for a 637-amino acid protein (molecular mass = 71.6 kDa) that resembles certain m6A-specific DNA-methyltransferases, particularly those that constitute the modification subunits of type I restriction-modification systems. The distal gene, bcgIB, codes for a 341-amino acid protein (molecular mass = 39.2 kDa) that resembles none of the sequences in the sequence data bases. The two genes overlap by several nucleotides. Alone, neither protein restricts or modifies DNA, but, together, they form a complex in the proportion A2B that does both. DNA binding assays showed that the DNA-protein complex can be formed only in the presence of both subunits, suggesting that the association of inactive subunits generates the active BcgI enzyme that can bind DNA and then either cleaves or methylates at target site.

Regulation of the ADE2 gene from Saccharomyces cerevisiae

Regulation of ADE2 gene expression was investigated in the yeast S. cerevisiae using translational fusions between this gene and the lacZ gene from E. coli. Expression was repressed in the presence of adenine and slightly increased under amino-acid starvation conditions. The promoters of the ADE2 gene, and of other genes involved in adenine biosynthesis, contain the hexanucleotide sequence TGACTC. A search for the hexanucleotide TGACTC in yeast promoter sequences revealed that many genes not related to amino-acid biosynthesis contain such sequences. We show here that these elements play a crucial role in ADE2 regulation since mutations in two such elements drastically reduced gene expression. Maximal expression required the transcriptional activators Bas1, Bas2 and Gcn4, whereas Yap1 had only minor effects.

Involvement of cyclic adenosine 3',5'-monophosphate in methylation during 1-methyladenine production by starfish ovarian follicle cells

Resumption of meiosis in starfish oocytes is induced by 1-methyladenine (1-MeAde) produced by ovarian follicle cells under the influence of a gonad-stimulating substance (GSS). With respect to 1-MeAde production, the effect of GSS on follicle cells results in the receptor-mediated formation of cyclic AMP (cAMP). It has also been reported that methylation is involved in 1-MeAde production by GSS. This study was undertaken to determine whether cAMP is the agent responsible for mediating methylation in 1-MeAde biosynthesis by isolated follicle cells of the starfish Asterina pectinifera. Methionine and selenomethionine enhanced 1-MeAde production by GSS in follicle cells. These stimulatory effects were dependent on the GSS concentration. Production of 1-MeAde by GSS was inhibited by ethionine and selenoethionine, competitive inhibitors of methionine. Like GSS, 1-MeAde production induced by concanavalin A, trypsin, and 3-isobutyl-1-methylxanthine (IBMX), which stimulated cAMP accumulation in follicle cells, was influenced by methionine and its related compounds. In contrast, although 1-methyladenosine (1-MeAde-R) induced 1-MeAde production by follicle cells without increasing cAMP levels, methionine and its related compounds had no effect. Use of [methyl-14C]methionine showed that a radiolabel was incorporated into 1-MeAde during incubation with GSS and IBMX, but not with 1-MeAde-R. These results strongly suggest that cAMP plays an important role in the process of methylation during 1-MeAde biosynthesis induced by GSS.

Do rhizobia produce cytokinins?

Two Rhizobium strains were cultured on a defined medium; one was a normal strain of the cowpea group (ANU240) while the other (IC3342) was an unusual but related strain of the same group which induced abnormal shoot development, including proliferation of lateral buds, in nodulated plants. Culture supernatants were examined for the presence of cytokinins by mass spectrometry using deuterium-labelled internal standards and by radioimmunoassay. In culture supernatants of both strains a range of cytokinins was detected and quantified, but N6-(2-isopentenyl)adenine (iP) and zeatin (Z) were the dominant cytokinins. The levels of Z and iP in supernatants of strain IC3342 were 26 and 8 times, respectively, those in supernatants of the strain ANU240. These results appear to provide the first unambiguous identifications of cytokinins in Rhizobium culture media. The cytokinin level in xylem sap of pigeonpea plants inoculated with strain IC3342 was markedly greater than that in plants inoculated with a normal nodulating strain. The abnormal proliferation of lateral buds in the former plants is probably linked to the elevation of cytokinin level in xylem sap caused by strain IC3342.

Cloning of three human multifunctional de novo purine biosynthetic genes by functional complementation of yeast mutations

Functional complementation of mutations in the yeast Saccharomyces cerevisiae has been used to clone three multifunctional human genes involved in de novo purine biosynthesis. A HepG2 cDNA library constructed in a yeast expression vector was used to transform yeast strains with mutations in adenine biosynthetic genes. Clones were isolated that complement mutations in the yeast ADE2, ADE3, and ADE8 genes. The cDNA that complemented the ade8 (phosphoribosylglycinamide formyltransferase, GART) mutation, also complemented the ade5 (phosphoribosylglycinamide synthetase) and ade7 [phosphoribosylaminoimidazole synthetase (AIRS; also known as PAIS)] mutations, indicating that it is the human trifunctional GART gene. Supporting data include homology between the AIRS and GART domains of this gene and the published sequence of these domains from other organisms, and localization of the cloned gene to human chromosome 21, where the GART gene has been shown to map. The cDNA that complemented ade2 (phosphoribosylaminoimidazole carboxylase) also complemented ade1 (phosphoribosylaminoimidazole succinocarboxamide synthetase), supporting earlier data suggesting that in some organisms these functions are part of a bifunctional protein. The cDNA that complemented ade3 (formyltetrahydrofolate synthetase) is different from the recently isolated human cDNA encoding this enzyme and instead appears to encode a related mitochondrial enzyme.

Adenine and pyrimidine genes of Aspergillus niger and evidence for a seventh linkage group

Mutants of Aspergillus niger requiring adenine and one mutant requiring cytosine were isolated after low-dose mutagenesis and enrichment. In addition we had mutants of two genes involved in the pyrimidine biosynthesis isolated as 5-fluoro-orotic acid-resistant mutants. The fifteen adenine-less mutants could be placed in seven complementation groups. From each group a representative mutant was analyzed in order to determine the linkage group by analysis of the mutants in a heterozygous diploid carrying markers in six linkage groups. AdeF could not be assigned to any one of these linkage groups and proved to be linked to nicB, oliC and cnxC, none of which could be placed in a linkage group. Thus, conclusive evidence was obtained for a seventh linkage group. As pyrA was used as selection marker for transformation, we constructed a pyrA strain with a linked marker which can be used in the genetic analysis of transformations.

Extent of formation of a dimeric adenine photoproduct in polynucleotides and DNA

Quantum yields are reported for the formation of a dimeric adenine photoproduct, A = A, in adenine homopolymers and DNA irradiated at 254 nm. The A = A content of irradiated samples was assayed by using reversed-phase HPLC to isolate the 4,6-diamino-5-guanidinopyrimidine (DGPY) which is produced from A = A on acid hydrolysis. Acid hydrolysates derived from DNA radiolabelled with [14C] 2'-deoxyadenosine were spiked with unlabelled DGPY before fractionation on HPLC and the recovered material was further purified by chromatography on Sephadex G-10 followed by co-crystallization with DGPY sulphate. Although A = A is formed with a relatively high quantum yield of 1.6 X 10(-3) mol einstein-1 in single-stranded poly(dA) the photoaddition reaction is strongly quenched in base-paired poly(dA).poly(dT) and undetectable in poly(rA).poly(dT). Respective quantum yields of 6 X 10(-5) and 9 X 10(-6) were estimated for the formation of A = A in single- and double-stranded E. coli DNA implying that the photoproduct has very limited biological significance. From studies with d(ApG), d(GpA), ApG, GpA, d(A)20 and d(A4G)4 it is concluded that adjacent guanine and adenine bases do not form a photoadduct analogous to A = A and also that guanine residues have no local or long-range quenching effect on photodimerization within A-A doublets.

Enzyme-pattern-targeted chemotherapy with tiazofurin and allopurinol in human leukemia

The hypothesis was tested that the increased IMP dehydrogenase activity in human myelocytic leukemic cells, and along with it guanylate biosynthesis, might be a sensitive target to chemotherapy by tiazofurin. 1. IMP dehydrogenase activity in normal leukocytes was 3.1 +/- 0.5 (means +/- S.E.) nmol/hr/mg protein and in leukemic cells it was elevated 15- to 41-fold. The activity of guanine phosphoribosyltransferase in normal leukocytes was 389 +/- 27 nmol/hr/mg protein and in the leukemic cells it increased 2.8- to 6.8-fold. 2. IMP dehydrogenase was purified 4,900-fold to homogeneity from rat hepatoma 3924A with a yield of 30%. The kinetic properties of the hepatoma enzyme were similar to those of the enzyme in human myelocytic leukemic blast cells because of the similarity of the Km's for IMP (23 microM), NAD (44 and 65 microM); the Ki for TAD was 0.1 microM in both enzymes. 3. There was a selectivity of the in vitro response to tiazofurin in human normal and leukemic leukocytes. When labeled tiazofurin was incubated with leukocytes from normal, healthy volunteers and from leukemic patients, the leukemic leukocytes made 20- to 30-fold more TAD and the GTP content decreased as compared to normal leukocytes. This procedure proved to be a suitable predictive test in a clinical setting because patients with positive tests responded to tiazofurin whereas those with negative ones did not. 4. The National Cancer Institute approved a chemotherapeutic phase I/II trial which concentrates on treatment of refractory acute myelocytic leukemia. Tiazofurin is infused in a 60-minute period with a pump to insure uniform delivery. A novel aspect of the trial was that it was directed primarily by the biochemical impact of tiazofurin on IMP dehydrogenase activity and GTP concentration and the tiazofurin doses were to be adjusted accordingly. Patients received allopurinol as a routine precaution against possible accumulation of uric acid in the kidney. 5. In the first eight patients, there was one complete remission, two entered the chronic phase, two entered into partial remission, one did not respond, and two were not evaluable. In the five patients who responded, there was a rapid, profound decrease in IMP dehydrogenase activity of the blast cells and a gradual decline in GTP concentrations. The blast cell count followed the decrease in the GTP concentration. The white blood cell count was largely preserved. 6. Bone marrow aspirates and peripheral blood samples showed that with tiazofurin treatment there was an induced differentiation of the myelocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of testosterone on purine synthesis de novo in rat perineal muscle in vivo

We examined in vivo the influence of testosterone on purine synthesis de novo, in the levator ani and gastrocnemius muscles of the rat. The hypoxanthine, adenine and guanine contents and the rate of incorporation of [14C]formate into these purine bases were determined in castrated adult and prepubertal rats (groups 1 and 2) both before and after orchiectomy and, in the second case, at different times after testosterone treatment. Substantially similar behavior was found in both groups, with some specific differences. The results showed an increase in the basal levels after castration (except for a dramatic decrease in adenine and a rise in the Gua/Ade molar ratio in prepubertal rats) and a return to basal levels after hormone administration, which was also accompanied by variations in the Gua/Ade molar ratio. The kinetics of purine nucleotide synthesis de novo in vivo and, specifically, of the overall reactions: IMP formation from PRib-PP, IMP----AMP and IMP----GMP, were followed by evaluating the incorporation curves of [14C]formate into hypoxanthine, adenine and guanine. Our results show that testosterone administration enhanced the incorporation rate and gave characteristic patterns: a diphasic cyclic oscillation of the Ade values in adult castrated rats, and single peaks having a specific shape in the other cases. The Gua/Ade labeling ratio was unchanged in castrated rats and increased in both groups during the first 5 days after testosterone treatment, after which values even fell below normal; in most cases, values overlapped the pattern of the Gua/Ade molar ratio. The specific profile of the curves indicated that testosterone initially accelerated the turnover of guanylic acid and in the second phase re-established the normal behavior and ratio of AMP and GMP formation. These results indicate that the 'inosinic branch point' was subject to regulation by testosterone. The profiles of the incorporation curves and of the Gua/Ade ratio were indicative of a primary and secondary response to hormone action.

2,8-Dihydroxyadenine lithiasis

2,8-Dihydroxyadenine (2,8-DHA) lithiasis is a form of kidney stone previously mistaken for uric acid because of identical reactivity in non-specific tests used routinely in stone analysis. Unlike uric acid, the stones crush easily and do not react with uricase. The biochemical basis for the defect is a deficiency of the enzyme adenine phosphoribosyltransferase (APRT). A complete deficiency has been reported in 29 patients from 11 countries. The number of stone formers reported in Japan (10 homozygotes, 16 heterozygotes) Austria (3), and Switzerland (2) suggests more efficient diagnosis in those countries. The defective enzyme in heterozygotes in Japan is a kinetic mutant demonstrable in intact not lysed cells. 20% of APRT-deficient subjects have been asymptomatic. An equal number have presented in acute renal failure, three of whom are now on dialysis. Formation of the nephrotoxic 2,8-DHA can be prevented by allopurinol. This underlines the importance of early diagnosis, since such severe renal damage should be avoidable.

Biosynthesis of 1-methyladenine by isolated segments of starfish ovaries

Acid-soluble 1-methyladenine (1-MeA) and an insoluble fraction containing 1-MeA were formed when radioactive L-methionine or adenine (A) were incubated with starfish ovary segments. Attempts to prepare free ribonucleic acid (RNA) from ovaries failed since it was strongly bonded to protein as ribonucleoprotein (RN-P) which was therefore used in studies involving RNA. Incubation of ovary segments with [8-14C]adenine-8 (A-8-14C) yielded both soluble 1-Me-A-8-14C and RN-P-8-14C, and similar incubation with L-[methyl-14C]methionine yielded soluble 1-MeA-14CH3 and RN-P-14CH3. Hydrolysis of RN-P-8-14C with 1 N HCl at 100 degrees yielded 91% of the initial radioactivity in the purine fraction, and of this 90% was in A, 9% in 1-MeA, and 1% in 4(5)-amino-5(4)-imidazole carboxamidine (AIMCAD). With RN-P-14CH3 the corresponding figures were 20, 45, 27, and 28%. Degradation of 1-MeA-8-14C or RN-P-8-14C with 6 N HCl at 110 degrees yielded radioactive AIMCAD which, on heating at pH 12, gave radioactive 4(5)-amino-5(4)-imidazole carboxamide (AICA). When 1-MeA-14CH3 or RN-P-14CH3 were similarly degraded, radioactive AIMCAD was formed, but the AICA possessed little or no radioactivity due to the loss of the radioactive methyl group. Addition of radial nerve factor (GSS) increased the yield of 1-MeA up to 19 times when radioactive L-methionine was substrate, but was ineffective with radioactive A. S-[8-14C]Adenosylmethionine was only about 3% as effective as L-[methyl-14C]methionine in supporting formation of 1-MeA, and its slight activity was not enhanced by GSS. Immature ovary segments were much more active than those from mature ovaries in synthesizing 1-MeA. The results support the contention that formation of free 1-MeA in starfish ovarian tissues involves methylation of adenine residues in a polynucleotide followed by liberation of 1-MeA by enzymatic hydrolysis.

Fluorometric assay using high-pressure liquid chromatography for the microsomal metabolism of certain substituted aliphatics to 1,N6-ethenoadenine-forming metabolites

Monohaloacetaldehydes and monohalooxiranes are early oxidative metabolites of several carcinogenic haloaliphatics. Since monohaloacetaldehydes and supposedly monohalooxiranes react with adenines to form fluorescent 1,N6-ethenoadenines, it was hypothesized that in vitro metabolic systems that produce an ethenoadenine-forming metabolite could be assayed quantitatively by trapping the metabolite in situ with an adenine and identifying it by its characteristic retention and fluorescence during HPLC. Bromoacetaldehyde was chosen as a model haloacetaldehyde to develop an assay based on this concept for measurements in a microsomal system. The optimal trapping reaction requires a postmetabolic step involving acidification and heating. Cyclic AMP was found to be a suitable adenine for the trapping reaction under these conditions. The chromatographic analysis utilizes tetrabutylammonium phosphate and a nonsilica reversed-phase stationary phase (Hamilton PRP-1). The chromatography is isocratic and allows an analysis time of less than 5 min per sample. The titration of bromoacetaldehyde in a microsomal system is affected by typically studied metabolic conditions: incubation time, pH, and protein concentration. Using this assay, the following were found to be metabolized by rat liver microsomes to etheno-adenine-forming products: 1,2-dibromoethane, 1,2-dichloroethane, cyclophosphamide, vinyl chloride, and acrylonitrile. Chloroacetone and 1,3-dichloroacetone also are fluorochromogenic without metabolism but the latter apparently forms a positively charged, nonetheno adduct. The proposed assay should be useful for in vitro metabolic studies of 1,2-dihaloethanes and mustards and has potential application for similar studies of monohalogenated ethanes, ethanols, and ethenes. The positive results with acrylonitrile suggest also that many types of substituted aliphatics may be studied with this proposed assay.

[Isolation and fractionation of DNA methylases from Mycobacterium butyricum]

Properties of total preparation of methylases from M. butyricum strain were studied using various methods of column chromatography. Distinct heterogeneity of the methylase preparation was demonstrated by gel filtration, anion exchange chromatography on diethyl aminoethyl cellulose and affinity chromatography on Sepharose blue. Several methylases, dissimilar both in physico-chemical properties and in their specificity to nitrogenous bases, were found in M. butyricum cells. In the strain studied methylases of adenine and cytosine were found, which were responsible for biosynthesis of 6-methyl adenine and 5-methyl cytosine in the acceptor DNA at the ratio 9 : 1.

Genetic analysis of red, adenine-requiring mutants of Candida albicans

A number of investigators have described the isolation of red, adenine-requiring mutants of Candida albicans. Other fungi have been shown to give rise to two phenotypically similar, but genetically distinct, types of red, adenine-requiring mutants. This paper is the first indication that the red adenine mutants of C. albicans can similarly be resolved into two distinct classes. It is also believed to be the first report of such a resolution in an imperfect fungus. The resolution of these two classes was achieved by applying three distinct parasexual, analytical methods to this imperfect, naturally diploid yeast. The methods employed were complementation analysis of fused protoplasts and two methods of recombination analysis, induced mitotic crossing over in heterozygous revertants and induced mitotic crossing over in the heterozygous tetraploid products of protoplast fusion. The recombination methods depended on linkage analysis between the ade loci and two loci, met1 (methionine) and arg1 (arginine). The three analytical methods supported the same resolution. The results support the generally accepted view that C. albicans is diploid since they indicate disomic inheritance at the ade1, ade2, and met1 loci.