Localization of human phosphoribosylpyrophosphate synthetase subunit I and II genes (PRPS1 and PRPS2) to different regions of the X chromosome and assignment of two PRPS1-related genes to autosomes

The expression spectrum of yak epididymal epithelial cells reveals the functional diversity of caput, corpus and cauda regions

Sperm undergo a series of changes in the epididymis region before acquiring the ability to move and fertilize, and the identification of genes expressed in a region-specific manner in the epididymis provides a valuable insight into functional differences between regions. We collected epididymal tissue from three yaks and cultured epithelial cells from the caput, corpus and cauda regions of the yak epididymis using the tissue block method. RNA sequencing analysis (RNA-seq) technology was used to detect gene expression in yak epididymal caput, corpus and cauda epithelial cells. The results showed that the DEGs were highest in the caput vs. corpus comparison, and lowest in the corpus vs. cauda comparison. Six DEGs were verified by real-time fluorescence quantitative PCR (qRT-PCR), consistent with transcriptome sequencing results. The significantly enriched DNA replication pathway in the caput vs. corpus was coordinated with cell proliferation, while upregulated DEGs such as POLD1 and MCM4 were found in the DNA replication pathway. The AMPK signaling pathway was found significantly enriched in the caput vs cauda, suggesting its involvement in sperm maturation and capacitation. The TGF beta signaling pathway was screened in the corpus vs cauda and is crucial for mammalian reproductive regulation. Upregulated DEGs (TGFB3, INHBA, INHBB) are involved in the TGF beta signaling pathway. This study provides a reference for culturing yak epididymal epithelial cells in vitro, and elucidates the transcriptional profiles of epithelial cells in different segments of the epididymis, revealing the regulatory and functional differences between different segments, providing basic data for exploring the molecular mechanism of yak sperm maturation and improving the reproductive capacity of high-altitude mammals.

Contribution of Model Organisms to Investigating the Far-Reaching Consequences of PRPP Metabolism on Human Health and Well-Being

Phosphoribosyl pyrophosphate synthetase (PRS EC 2.7.6.1) is a rate-limiting enzyme that irreversibly catalyzes the formation of phosphoribosyl pyrophosphate (PRPP) from ribose-5-phosphate and adenosine triphosphate (ATP). This key metabolite is required for the synthesis of purine and pyrimidine nucleotides, the two aromatic amino acids histidine and tryptophan, the cofactors nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+), all of which are essential for various life processes. Despite its ubiquity and essential nature across the plant and animal kingdoms, PRPP synthetase displays species-specific characteristics regarding the number of gene copies and architecture permitting interaction with other areas of cellular metabolism. The impact of mutated PRS genes in the model eukaryote Saccharomyces cerevisiae on cell signalling and metabolism may be relevant to the human neuropathies associated with PRPS mutations. Human PRPS1 and PRPS2 gene products are implicated in drug resistance associated with recurrent acute lymphoblastic leukaemia and progression of colorectal cancer and hepatocellular carcinoma. The investigation of PRPP metabolism in accepted model organisms, e.g., yeast and zebrafish, has the potential to reveal novel drug targets for treating at least some of the diseases, often characterized by overlapping symptoms, such as Arts syndrome and respiratory infections, and uncover the significance and relevance of human PRPS in disease diagnosis, management, and treatment.

Untargeted LC-MS-based metabonomic analysis of the effect of photoperiod on the testes of broiler roosters

Photoperiod is an important factor that stimulates the reproductive performance of broiler breeder roosters. However, the mechanism by which photoperiod affects the reproductive performance of broiler breeder roosters has not been fully studied. To study the effects of different photoperiods on the reproductive performance of broiler breeder roosters, 120 Arbor Acres broiler breeder roosters aged 20 weeks were randomly assigned to three groups (n = 40), and the three groups were treated with different photoperiod regimes: control (CTR; 12.5 h of light and 11.5 h of dark, 12.5 L: 11.5 D), short day (SD; 16 L: 8 D) and long day (LD; 8 L: 16 D). Serum and testes were collected after 4 weeks of feeding, and testosterone-related indices were detected. We found that testosterone synthesis in the testes of broiler roosters was boosted with prolonged of photoperiod. Subsequently, metabonomics was used to identify the differential endogenous metabolites that may affect the function of the testes in breeder roosters. We found compared with other groups, the concentrations of creatine, uridine monophosphate, phosphoribosyl pyrophosphate, dCMP, α-D-glucose and citric acid in the SD group decreased significantly (p < 0.05), and glyoxylic acid, D-ribose 5-phosphate, deoxyuridine and orotic acid in the SD group increased significantly (p < 0.05), while the CTR group and LD group showed no significant difference (p > 0.05). The concentrations of linoleic acid and α-linolenic acid in the LD group were increased significantly (p < 0.05) than those in the CTR and SD groups. Compared with the CTR group, the concentrations of histamine in the SD and LD groups were significant increased (p < 0.05). The 13 of the different metabolites could be used as candidate biomarkers for different photoperiods affecting testosterone synthesis, may be used to molecular breeding of high reproductive performance broiler roosters.

Role of PRPS2 as a prognostic and therapeutic target in osteosarcoma

AIMS

Osteosarcoma (OS) is the most common primary malignant tumour of the bone. However, further improvement in survival has not been achieved due to a lack of well-validated prognostic markers and more effective therapeutic agents. Recently, the c-Myc-phosphoribosyl pyrophosphate synthetase 2 (PRPS2) pathway has been shown to promote nucleic acid metabolism and cancer cell proliferation in malignant melanoma; phosphorylated mammalian target of rapamycin (p-mTOR) has been upregulated and an effective therapeutic target in OS. However, the p-mTOR-PRPS2 pathway has not been evaluated in OS.

METHODS

In this study, the expression level of PRPS2, p-mTOR and marker of proliferation (MKI-67) was observed in a cohort of specimens (including 236 OS cases and 56 control samples) using immunohistochemistry, and the association between expression level and clinicopathological characteristics of patients with OS was analysed.

RESULTS

PRPS2 protein level, which is related to tumour proliferation, was higher in OS cells (p=0.003) than in fibrous dysplasia, and the higher PRPS2 protein level was associated with a higher tumour recurrence (p=0.001). In addition, our statistical analysis confirmed that PRPS2 is a novel, independent prognostic indicator of OS. Finally, we found that the expression of p-mTOR was associated with the poor prognosis of patients with OS (p<0.05).

CONCLUSIONS

PRPS2 is an independent prognostic marker and a potential therapeutic target for OS.

Phosphoribosyl-pyrophosphate synthetase 2 (PRPS2) depletion regulates spermatogenic cell apoptosis and is correlated with hypospermatogenesis

Phosphoribosyl-pyrophosphate synthetase 2 (PRPS2) is a rate-limiting enzyme and plays an important role in purine and pyrimidine nucleotide synthesis. Recent studies report that PRPS2 is involved in male infertility. However, the role of PRPS2 in hypospermatogenesis is unknown. In this study, the relationship of PRPS2 with hypospermatogenesis and spermatogenic cell apoptosis was investigated. The results showed that PRPS2 depletion increased the number of apoptotic spermatogenic cells in vitro. PRPS2 was downregulated in a mouse model of hypospermatogenesis. When PRPS2 expression was knocked down in mouse testes, hypospermatogenesis and accelerated apoptosis of spermatogenic cells were noted. E2F transcription factor 1 (E2F1) was confirmed as the target gene of PRPS2 and played a key role in cell apoptosis by regulating the P53/Bcl-xl/Bcl-2/Caspase 6/Caspase 9 apoptosis pathway. Therefore, these data indicate that PRPS2 depletion contributes to the apoptosis of spermatogenic cells and is associated with hypospermatogenesis, which may be helpful for the diagnosis of male infertility.

Valproic acid- and lithium-sensitivity in prs mutants of Saccharomyces cerevisiae

Prs [PRPP (phosphoribosyl pyrophosphate) synthetase] catalyses the transfer of pyrophosphate from ATP to ribose 5-phosphate, thereby activating the pentose sugar for incorporation into purine and pyrimidine nucleotides. The Saccharomyces cerevisiae genome contains five genes, PRS1-PRS5, whose products display characteristic PRPP and bivalent-cation-binding sites of Prs polypeptides. Deletion of one or more of the five PRS genes has far-reaching and unexpected consequences, e.g. impaired cell integrity, temperature-sensitivity and sensitivity to VPA (valproic acid) and LiCl. CTP pools in prs1Delta and prs3Delta are reduced to 12 and 31% of the wild-type respectively, resulting in an imbalance in phospholipid metabolism which may have an impact on the intracellular inositol pool which is affected by the administration of either VPA or LiCl. Overexpression of CTP synthetase in prs1Delta prs3Delta strains partially reverses the VPA-sensitive phenotype. Yeast two-hybrid screening revealed that Prs3 and the yeast orthologue of GSK3 (glycogen synthase kinase 3), Rim11, a serine/threonine kinase involved in several signalling pathways, interact with each other. Furthermore, Prs5, an essential partner of Prs3, which also interacts with GSK3 contains three neighbouring phosphorylation sites, typical of GSK3 activation. These studies on yeast PRPP synthetases bring together and expand the current theories for the mood-stabilizing effects of VPA and LiCl in bipolar disorder.

Phosphoribosylpyrophosphate synthetase and the regulation of phosphoribosylpyrophosphate production in human cells

between purine nucleoside diphosphate inhibition and inorganic phosphate (Pi) activation; and intracellular concentration of the PRS1 isoform. The operation of additional determinants of rates of PRPP synthesis in human cells is suggested by: (1) multiple PRS isoforms with distinctive physical and kinetic properties; (2) nearly immediate activation of intracellular PRPP synthesis in response to mitogens, growth-promoters, and increased intracellular Mg2+ concentrations; (3) tissue-specific differences in PRS1 and PRS2 transcript and isoform expression; and (4) reversible association of PRS subunits with one another and/or with PRS-associated proteins (PAPs), as a result of which the catalytic and perhaps regulatory properties of PRS isoforms are modified.

Genetic disorders and urolithiasis

A recent analysis of the McKusick's On-Line Mendelian Inheritance in Man (OMIM) database revealed over 30 genetic or putatively genetic conditions in which urolithiasis contributes to the disease pathology at least to some extent. There is wide clinical, biochemical, and genetic heterogeneity in many of these conditions.

Accelerated transcription of PRPS1 in X-linked overactivity of normal human phosphoribosylpyrophosphate synthetase

Phosphoribosylpyrophosphate (PRPP) synthetase (PRS) superactivity is an X-linked disorder characterized by gout with overproduction of purine nucleotides and uric acid. Study of the two X-linked PRS isoforms (PRS1 and PRS2) in cells from certain affected individuals has shown selectively increased concentrations of structurally normal PRS1 transcript and isoform, suggesting that this form of the disorder involves pretranslational dysregulation of PRPS1 expression and might be more appropriately termed overactivity of normal PRS. We applied Southern and Northern blot analyses and slot blotting of nuclear runoffs to delineate the process underlying aberrant PRPS1 expression in fibroblasts and lymphoblasts from patients with overactivity of normal PRS. Neither PRPS1 amplification nor altered stability or processing of PRS1 mRNA was identified, but PRPS1 transcription was increased relative to GAPDH (3- to 4-fold normal in fibroblasts; 1.9- to 2.4-fold in lymphoblasts) and PRPS2. Nearly coordinate relative increases in each process mediating transfer of genetic information from PRPS1 transcription to maximal PRS1 isoform expression in patient fibroblasts further supported the idea that accelerated PRPS1 transcription is the major aberration leading to PRS1 overexpression. In addition, modulated relative increases in PRS activities at suboptimal Pi concentration and in rates of PRPP and purine nucleotide synthesis in intact patient fibroblasts indicate that despite an intact allosteric mechanism of regulation of PRS activity, PRPS1 transcription is a major determinant of PRPP and purine synthesis. The genetic basis of disordered PRPS1 transcription remains unresolved; normal- and patient-derived PRPS1s share nucleotide sequence identity at least 850 base pairs 5' to the consensus transcription initiation site.

Rat liver phosphoribosylpyrophosphate synthetase is activated by free Mg2+ in a manner that overcomes its inhibition by nucleotides

Phosphoribosylpyrophosphate synthetase is activated by Pi and free Mg2+ as an essential activator and inhibited by nucleotides, especially ADP and GDP. The rat liver enzyme is a complex aggregate of two highly homologous catalytic subunits (PRS I and PRS II) and two associated proteins (PAP39 and PAP41). PRS I is more sensitive to inhibition by ADP and GDP than is PRS II. The native liver enzyme showed a weaker sensitivity to inhibition by nucleotides than expected from its composition. To further understand the regulation of the liver enzyme, kinetic studies of each subunit component and the liver enzyme regarding Mg2+ activation and inhibition by ADP and GDP were carried out. Assay conditions were designed to keep free Mg2+ at constant concentrations. (1) GDP, as MgGDP, did not affect the apparent Km values of PRS I for MgATP and ribose-5-phosphate but did dramatically increase the apparent Ka value for free Mg2+. (2) In contrast, ADP, as MgADP, increased the Km value for MgATP of PRS I as well as the Ka value for free Mg2+. (3) High concentrations of free Mg2+ almost completely nullified the inhibitory effect of MgGDP and partly that of MgADP on PRS I. (4) At low free Mg2+ concentrations within the physiological range, inhibition by the nucleotides is of physiological significance and conversely, variation in free Mg2+ concentrations critically affects the enzyme activity in the presence of inhibitory nucleotides. (5) The response of PRS II and the native liver enzyme is similar to that of PRS I, while the effects of MgGDP and MgADP were smaller than that on PRS I. (6) We propose that MgGDP binds to a regulatory site of PRS I and PRS II and MgADP to the substrate MgATP site and also the regulatory site. The allosteric interaction of the regulatory site and the Mg2+ binding site is also considered.

Regulation of the human inosine monophosphate dehydrogenase type I gene. Utilization of alternative promoters

Catalysis of guanine nucleotide formation from IMP in the de novo purine synthetic pathway is carried out by two isoforms of the enzyme inosine monophosphate dehydrogenase (IMPDH) that are catalytically indistinguishable but are encoded by separate genes. In order to assess the potential for cell type-specific expression of IMPDH activity, we have characterized the IMPDH type I gene and identified three major RNA transcripts that are differentially expressed from three different promoters. A 4.0-kilobase pair (kb) mRNA containing 1.3 kb of 5'-untranslated region is expressed in activated peripheral blood lymphocytes and to a far lesser extent in cultured tumor cell lines. The P1 promoter that regulates the transcription of this mRNA has a high degree of sequence identity to an Alu repetitive sequence. A transcript of 2.7 kb is found in a subset of the tumor cell lines examined, whereas a 2.5-kb mRNA species is universally expressed and is the prevalent mRNA in most cell lines and tissues. The relative strengths of the three promoter regions and the effects of variable extents of 5'-flanking sequence on the P3 promoter differ in Jurkat T, as compared with Raji B lymphoid cell lines, demonstrating a complex cell type-specific transcriptional regulation of IMPDH type I gene expression.

Linkage analysis in a family with the Opitz GBBB syndrome refines the location of the gene in Xp22 to a 4 cM region

The Opitz GBBB syndrome (OS) is characterized in part by widely spaced inner ocular canthi and hypospadias. Recently, linkage analysis showed that the gene for the X-linked form to be located in an 18 cM region spanning Xp22. We have now conducted linkage analysis in a family previously published as having the BBB syndrome and found tight linkage to DXS7104 (Z = 3.3, theta = 0.0). Our data narrows the candidate region to 4 cM and should facilitate the identification and characterization of one of the genes involved in midline development.

Cloning and sequencing of rat cDNA for the 41-kDa phosphoribosylpyrophosphate synthetase-associated protein has a high homology to the catalytic subunits and the 39-kDa associated protein

Rat liver phosphoribosylpyrophosphate synthetase is a complex aggregate of 34-kDa catalytic subunits (PRS I and II) and 39- and 41-kDa associated proteins (PAP39 and 41). When the rat cDNA encoding PAP41 was isolated, the deduced protein sequence was seen to contain 369 amino acids with a calculated molecular mass of 41130. PAP41 has a 79 and 49% identity with PAP39 and PRSs, respectively. When conservative substitutions are included, PAP41 and the three other components have a 66% homology. PAP41 shares some common features with PAP39 and the two proteins form the PAP subfamily. The mRNA of PAP41 is present in all rat tissues we examined.

Multi-system signs and symptoms in X-linked ataxia carriers

Neurological, auditory, vestibular and ocular motor examinations were performed on 3 definite and 3 possible heterozygous carriers of a previously described X-linked multi-system disorder with early childhood onset, rapid progression and a fatal outcome (Arts et al., 1993). The symptoms, i.e., delayed motor development, ataxia, hearing loss and subnormal intelligence, were so evident in 2 of the possible carriers that they could be redesignated as probable carriers. Other symptoms in the definite and probable carriers were clubfeet, dysarthria, intention tremor and abnormal gait, while their signs included dysdiadochokinesia, ataxic paraplegia, abnormal muscle tendon reflexes and extensor plantar responses. All the symptomatic carriers developed moderate-to-severe sensorineural hearing loss with normal stapedial reflexes and brain stem auditory evoked potentials (BAEPs) in those in whom this could be evaluated. Speech discrimination was disproportionally poor unilaterally in one case from whom no BAEPs could be obtained because of her degree of hearing loss. Various combinations were found of high gain of the vestibulo-ocular reflex, spontaneous nystagmus and directional preponderance of vestibularly evoked nystagmus, slowing, hypometria or multi-stepping of saccades, saccadic intrusions of eye movements (macro square wave jerks, double saccadic pulses), impairment of smooth pursuit eye movements and optokinetic nystagmus, and failure of visual fixation suppression of vestibularly evoked nystagmus. Such findings indicate major involvement of the (vestibulo)cerebellum and the vermis. MRI in one carrier showed mild cerebellar atrophy.

Overexpression of the normal phosphoribosylpyrophosphate synthetase 1 isoform underlies catalytic superactivity of human phosphoribosylpyrophosphate synthetase

To define the enzymatic and genetic basis of X-linked phosphoribosylpyrophosphate synthetase (PRS) catalytic superactivity, we measured concentrations of X-linked PRS1 and PRS2 isoforms in cultured fibroblasts and lymphoblasts by immunoblotting after separation by polyacrylamide-urea isoelectric focusing. PRS1 comprised >80% of measurable PRS isoforms in all fibroblast strains, but PRS1 concentrations in cells from six affected males exceeded those in normal cells by 2-6-fold. PRS absolute specific activities (activity per mg of PRS isoforms) were comparable in all fibroblast strains and in purified recombinant normal PRS1, confirming selectively increased levels of PRS1 isoform as the enzymatic basis of PRS catalytic superactivity. Cloning, sequencing, and expression of normal subject- and patient-derived PRS cDNAs predicted normal translated region sequences for both PRS isoforms and revealed no differences in catalytic properties of recombinant PRS1. Normal and patient PRPS1 transcribed but untranslated DNA sequences were also identical. Northern blot analysis showed selective increase in relative concentrations of PRS1 transcripts in patient fibroblasts. In PRS catalytic superactivity, overexpression of the normal PRS1 isoform thus appears to result from an altered pretranslational mechanism of PRPS1 expression. In lymphoblasts, however, expression of this alteration is attenuated, explaining the absence of phenotypic expression of PRS catalytic superactivity in these cells.

Cloning and sequencing of human complementary DNA for the phosphoribosylpyrophosphate synthetase-associated protein 39

A human cDNA encoding a human homologue of the rat phosphoribosylpyrophosphate synthetase-associated protein of 39 kDa was isolated. The deduced protein contains 356 amino acids and has calculated molecular mass of 38561. The amino acid sequence is 98% identical to that of the rat. The corresponding mRNA is present in all human tissues examined.

The genetic and functional basis of purine nucleotide feedback-resistant phosphoribosylpyrophosphate synthetase superactivity

The genetic and functional basis of phosphoribosylpyrophosphate synthetase (PRS) superactivity associated with purine nucleotide inhibitor-resistance was studied in six families with this X chromosome-linked purine metabolic and neurodevelopmental disorder. Cloning and sequencing of PRS1 and PRS2 cDNAs, derived from fibroblast total RNA of affected male patients by reverse transcription and PCR amplification, demonstrated that each PRS1 cDNA contained a distinctive single base substitution predicting a corresponding amino acid substitution in the PRS1 isoform. Overall, the array of substitutions encompassed a substantial portion of the translated sequence of PRS1 cDNA. Plasmid-mediated expression of variant PRS1 cDNAs in Escherichia coli BL21 (DE3/pLysS) yielded recombinant mutant PRS1s, which, in each case, displayed a pattern and magnitude of purine nucleoside diphosphate inhibitor-resistance comparable to that found in cells of the respective patient. Kinetic analysis of recombinant mutant PRS1s showed that widely dispersed point mutations in the X chromosome-linked PRPS1 gene encoding the PRS1 isoform result in alteration of the allosteric mechanisms regulating both enzyme inhibition by purine nucleotides and activation by inorganic phosphate. The functional consequences of these mutations provide a tenable basis for the enhanced production of phosphoribosylpyrophosphate, purine nucleotides, and uric acid that are the biochemical hallmarks of PRS superactivity.

Mammalian phosphoribosyl-pyrophosphate synthetase

PRPP synthetase from rat liver exists as large molecular weight aggregates composed of at least three different components. Cloning of cDNA for the catalytic subunit revealed the presence of two highly homologous isoforms of 34 kDa, designated as PRS I and PRS II. Northern blot analysis showed tissue-differential expression of the two isoform genes. cDNA was expressed in E. coli and studies on the recombinant isoforms showed differences in sensitivity to inhibition by ADP and GDP and to heat inactivation. The rat gene for PRS I has 22 kb and is split into 7 exons. cDNAs for human enzymes were also cloned. Human genes for PRS I and PRS II are localized at different regions on the X-chromosome and their promoter regions were examined. Another component, PRPP synthetase-associated protein of 39 kDa (PAP39), was cloned from cDNA library of the rat liver. The deduced amino acid sequence of PAP39 is remarkably similar to those of PRS I and PRS II. Evidence indicated molecular interaction between PAP39 and the catalytic subunits and an inhibitory effect of PAP39 on the catalytic activity. Expression of the PAP39 gene is tissue-differential like the PRS genes, indicating that the composition of PRPP synthetase may differ with the tissue, hence properties of the enzyme would differ. Further studies on these components and their interaction are expected to reveal various mechanisms governing mammalian PRPP synthetase.

Linkage of phosphoribosylpyrophosphate synthetases 1 and 2, Prps1 and Prps2, on the mouse X chromosome

The X Chromosome (Chr) genes for phosphoribosylpyrophosphate synthetases 1 and 2, Prps1 and Prps2, were mapped on the mouse X Chr with interspecific backcrosses between C57BL/6 (B6) and M. spretus (S). Southern analysis showed that Prps1 mapped between Plp and DXWas31, a mouse X Chr region that is homologous to Xq21-24 on the human X Chr while Prps2 mapped between DXWas31 and Amg, a region that is homologous to the map position of PRPS2 on Xp22 of the human X Chr. Additionally, other restriction fragments highlighted by PRS II showed autosomal segregation. In situ hybridization and FISH analysis of metaphase chromosome spreads prepared from lymphocytes of B6 or S male mice confirmed that there were in fact two different locations on the X Chr, X F1-2 and X F2-3 for Prps1 and 2 respectively, as well as two autosomal sites for Prps-like genes.

Molecular characterization of phosphoribosylpyrophosphate synthetase from Leishmania donovani

The phosphoribosylpyrophosphate synthetase (PRS) enzyme from parasitic protozoa plays a critical role in the acquisition of exogenous purine bases by providing the phosphoribosylpyrophosphate substrate for phosphoribosylation. To characterize a PRS enzyme from parasitic protozoa, the prs gene was isolated from a genomic library of Leishmania donovani DNA. A 1936-bp SalI fragment was sequenced that encompassed an open reading frame of 1113 nucleotides encoding a polypeptide of 371 amino acids and 40 787 Da. After gap alignment, the leishmanial PRS exhibited 40-42% amino acid identity with a variety of mammalian and prokaryotic PRSs. L. donovani PRS also contained an approx. 20-amino acid stretch that was highly homologous to the phosphoribosylpyrophosphate binding domains of mammalian phosphoribosyltransferase enzymes. Two prs-specific transcripts of 2.6 and 2.1 kb were detected by Northern analysis, and Southern blots of genomic DNA implied that the prs locus was not tandemly repeated in the L. donovani genome. PRS activity was detected in L. donovani extracts, and apparent Km values of approx. 30 microM and approx. 1 mM were calculated for ribose-5-phosphate and ATP, respectively. PRS was sensitive to inhibition by AMP and ADP but refractory to IMP, GMP, GTP, CTP, and UTP. The high apparent Km value of the parasite enzyme for ATP and its insensitivity to inhibition by many nucleotides suggested that kinetic differences between the L. donovani and human PRSs could provide an avenue for rational therapeutic manipulation of parasitic disease. The isolation of the L. donovani prs gene now provides an opportunity to genetically dissect the determinants responsible for the function and regulation of this indispensable enzyme of purine and pyrimidine metabolism in a genus of parasitic protozoa.

Structure and expression of human and rat D2 dopamine receptor genes

D2 dopamine receptor may be related with the pathogenesis of Parkinson's disease and schizophrenia. Furthermore, the antipsychotic drugs have high affinity for D2 dopamine receptor. We carried out the cloning of the genomic DNA for human D2 dopamine receptor and clarified the structure of this gene. Our isolated gene spans about 15 kbp and consists of seven exons interrupted by six introns. However, putative first exon was not yet identified. Spot blot hybridization analysis of cell sorter fractionated human chromosomal DNA with D2 receptor genomic DNA revealed the localization of this gene in the chromosome 11 fraction. We analyzed human genomic DNA by Southern blot hybridization with D2 dopamine receptor genomic DNA as a probe, but so far we could not find RFLP. Northern blot analyses of brain RNA of several animals and rat brain RNA after various treatments were carried out. Developmental changes of D2 dopamine receptor mRNA were observed in the rat brains.

cDNA cloning and chromosome assignment of the gene for human brain 14-3-3 protein eta chain

We present the nucleotide sequence of a cDNA clone of mRNA encoding human 14-3-3 protein, a protein kinase-dependent activator of tyrosine and tryptophan hydroxylases and an endogenous inhibitor of protein kinase C. The 1,730-nucleotide sequence of the cloned cDNA contains 191 bp of a 5'-noncoding region, the complete 738 bp of coding region, and 801 bp of a 3'-noncoding region containing three canonical polyadenylation signals. The 14-3-3 protein eta chain cDNA encoded a polypeptide of 246 amino acids with a predicted molecular weight 28,196. The predicted amino acid sequence of human 14-3-3 protein eta was highly homologous to that of previously reported bovine and rat 14-3-3 proteins with only two amino acid differences. The sequence carries structural features as putative regions responsible for activation of tyrosine and tryptophan hydroxylases and for inhibition of Ca2+/phospholipid-dependent protein kinase C. Northern blot analysis demonstrated widespread expression of the 14-3-3 protein eta chain in cultured cell lines derived from various human tumors. These findings suggest the conservative functions of the 14-3-3 protein among species. Spot blot hybridization analysis with flow-sorted chromosomes showed that the human 14-3-3 protein eta chain gene is assigned to chromosome 22.

Promoter regions of the human X-linked housekeeping genes PRPS1 and PRPS2 encoding phosphoribosylpyrophosphate synthetase subunit I and II isoforms

The 5' regions of the human phosphoribosylpyrophosphate synthetase subunit I and II genes (PRPS1 and PRPS2, respectively) were isolated and sequenced. A comparison of the nucleotide sequences between human and rat PRPS1 genes revealed that the sequences around the transcription initiation sites were conserved over 56 nucleotides, and that a TATA-like sequence, a CCAAT box and three putative Sp1 binding sites were present at almost the same positions in the GC-rich sequences. Two major transcription initiation sites were localized in the human PRPS1, one of the two was located 27 nucleotides downstream from the TATA-like sequence, while the upstream initiation site was in the TATA-like sequence. The promoter region of the human PRPS2 gene was also GC-rich and contained a TATA-like sequence, four Sp1 binding sites and a homopyrimidine stretch. The initiation sites were localized at 90 nucleotides upstream from the ATG initiation codon. Chloramphenicol acetyltransferase (CAT)/promoter fusion assays showed that a 2.0 kb region (human PRPS1) and a 1.1 kb region (human PRPS2) possessed the promoter activities in four cell lines. The CAT activities in the three human cell lines tended to correlate with the steady-state mRNA levels of the PRPS1 and PRPS2 genes. These results suggest that the 5' flanking regions cloned contribute to the cell-differential expression of these two genes.

Physical mapping of loci in the distal half of the short arm of the human X chromosome: implications for the spreading of X-chromosome inactivation

The relative order of 11 loci in the distal half of the short arm of the human X chromosome was examined using a panel of somatic cell hybrids containing structurally rearranged X chromosomes. The results show that the gene for phosphoribosylpyrophosphate synthetase 2 (PRPS2) is located between ZFX (zinc finger protein, X-linked) and STS (steroid sulfatase). The results also confirm the localization of ZFX distal to POLA (alpha-DNA polymerase). Previous studies have shown that STS and ZFX escape X-inactivation whereas POLA undergoes inactivation. Evaluation of PRPS2 expression in somatic cell hybrids containing inactive human X chromosomes showed that PRPS2 undergoes X-inactivation. These results provide further evidence for interspersion of loci that do and do not undergo X-inactivation on the human X chromosome.

Cloning of cDNAs for human phosphoribosylpyrophosphate synthetases 1 and 2 and X chromosome localization of PRPS1 and PRPS2 genes

Cloned cDNAs representing the entire, homologous (80%) translated sequences of human phosphoribosylpyrophosphate synthetase (PRS) 1 and PRS 2 cDNAs were utilized as probes to localize the corresponding human PRPS1 and PRPS2 genes, previously reported to be X chromosome linked. PRPS1 and PRPS2 loci mapped to the intervals Xq22-q24 and Xp22.2-p22.3, respectively, using a combination of in situ chromosomal hybridization and human x rodent somatic cell panel genomic DNA hybridization analyses. A PRPS1-related gene or pseudogene (PRPS1L2) was also identified using in situ chromosomal hybridization at 9q33-q34. Human HPRT and PRPS1 loci are not closely linked. Despite marked cDNA and deduced amino acid sequence homology, human PRS 1 and PRS 2 isoforms are encoded by genes widely separated on the X chromosome.

Selective activation of testis-specific genes in cultured rat spermatogenic cells

During mammalian spermatogenesis the isozyme pattern of a glycolytic enzyme, phosphoglycerate kinase (PGK; ATP: 3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3), changes from the somatic-type PGK-1 to the testis-specific PGK-2, and this change has been suggested to involve transcription switch. We have isolated genomic DNA fragments which code for the mouse PGK isozymes and determined the transcription start site of each gene. The results demonstrate that transcriptions of the two PGK genes are initiated at multiple sites under the control of TATA box-lacking promoters. The putative promoter regions of the two genes contain several distinct sequences known as the CCAAT box and the GC box which possibly bind CCAAT-binding proteins and Sp1, respectively. We next developed a culture system in which spermatogenic gene expression is partly reproduced. When spermatogenic cells of 20-day-old rats were cultured, transcripts from PGK-2 and another spermatogenic gene PRPS3 became detectable, while expression of other non-spermatogenic genes did not significantly change during culture. These results suggest that two spermatogenic genes PGK-2 and PRPS3 were activated in culture according to a developmental program of spermatogenesis. Thus, this culture system may be useful for studying the molecular mechanism underlying mammalian spermatogenic gene expression.

The human ATP synthase beta subunit gene: sequence analysis, chromosome assignment, and differential expression

In humans, the functional F0F1-ATP synthase beta subunit gene is located on chromosome 12 in the p13----qter region. Other partially homologous sequences have been detected on chromosomes 2 and 17. The bona fide beta subunit gene has 10 exons encoding a leader peptide of 49 amino acids and a mature protein of 480 amino acids. Thirteen Alu family DNA repeats are found upstream from the gene and in four introns. The gene has four "CCAAT" sequences upstream and in close proximity to the transcriptional initiation site. A 13-bp motif is found in the 5' nontranscribed region of both the beta subunit gene and an ADP/ATP translocator gene that is expressed in high levels in cardiac and skeletal muscle. Analysis of the beta subunit mRNA levels reveals marked differences among tissues. The highest levels are found in heart, lower levels in skeletal muscle, and the lowest levels in liver and kidney. These findings suggest that the tissue-specific levels of ATP synthase beta subunit mRNA may be generated through transcriptional control.

Isolation of cDNAs encoding a substrate for protein kinase C: nucleotide sequence and chromosomal mapping of the gene for a human 80K protein

An acidic phosphoprotein of Mr 80,000, the 80K protein, is a substrate for protein kinase C in fibroblasts and epidermal carcinoma cells. We purified the 80K protein from human squamous carcinoma Ca9-22 cells and fractionated it into two distinct molecular species, designated the 80K-L and 80K-H proteins. The amino acid sequences of the NH2-terminal region and cyanogen bromide-cleaved fragments of the 80K-H protein were determined and a corresponding oligonucleotide sequence was synthesized. Using this as a probe, two cDNA clones, lambda 80H-1 and lambda 80H-2, were selected from a lambda gt10 cDNA library from human A431 cells. The nucleotide sequence has an open reading frame of 1581 nucleotides encoding a protein of 527 amino acids. The deduced amino acid sequence revealed an extremely Glu-rich region. RNA blot analysis with the lambda 80H-1 cDNA clone detected two polyadenylated transcripts of 2.3 and 3.5 kb in Ca9-22 cells. Spot blot hybridization using flow-sorted human chromosomes provided evidence that the gene (G19P1) encoding 80K-H protein maps to human chromosome 19.