Regional localization of the human genes for S-adenosylhomocysteine hydrolase (cen----q131) and adenosine deaminase (q131----qter) on chromosome 20

Importance of the trans-sulfuration pathway in cancer prevention and promotion

The trans-sulfuration pathway is a biochemical mechanism that links methionine metabolism to the biosynthesis of cellular redox-controlling molecules, like cysteine, glutathione, and taurine. While there is some knowledge about the metabolic intermediates and enzymes that participate in trans-sulfuration, little is known about the physiological importance of this mechanism. Deficiencies within the trans-sulfuration pathway induces (i) the generation of reactive species of oxygen (ROS) and halogens (RHS), (ii) homocyst(e)ine accumulation, and (iii) the synthesis of proinflammatory molecules by macrophages, and contribute to humans pathologies like atherosclerosis and tumor development. In this review we outline the role of this biochemical pathway in tumor development and analyze current findings on the role of trans-sulfuration in mammalian physiology. The potential relationship between chronic inflammation, and tumor and atherosclerotic development are discussed.

A functional genetic variation of adenosine deaminase affects the duration and intensity of deep sleep in humans

Slow, rhythmic oscillations (<5 Hz) in the sleep electroencephalogram may be a sign of synaptic plasticity occurring during sleep. The oscillations, referred to as slow-wave activity (SWA), reflect sleep need and sleep intensity. The amount of SWA is homeostatically regulated. It is enhanced after sleep loss and declines during sleep. Animal studies suggested that sleep need is genetically controlled, yet the physiological mechanisms remain unknown. Here we show in humans that a genetic variant of adenosine deaminase, which is associated with the reduced metabolism of adenosine to inosine, specifically enhances deep sleep and SWA during sleep. In contrast, a distinct polymorphism of the adenosine A(2A) receptor gene, which was associated with interindividual differences in anxiety symptoms after caffeine intake in healthy volunteers, affects the electroencephalogram during sleep and wakefulness in a non-state-specific manner. Our findings indicate a direct role of adenosine in human sleep homeostasis. Moreover, our data suggest that genetic variability in the adenosinergic system contributes to the interindividual variability in brain electrical activity during sleep and wakefulness.

The emerging role of adenosine deaminases in insects

Adenosine deaminases catalyze the deamination of adenosine and deoxyadenosine into their respective inosine nucleosides. Recent sequencing of the genomes of several model organisms and human reveal that Metazoa usually have more than one adenosine deaminase gene. A deficiency in the gene encoding the major enzyme is lethal in mouse and Drosophila and leads to severe combined deficiency (SCID) in human. In these organisms, enzyme deficiency causes increased adenosine/deoxyadenosine concentration in body fluids and some organs. Elevated levels of adenosine and deoxyadenosine are toxic to certain mammalian and insect cells, and it was shown for human and mouse that it is a primary cause of pathophysiological effects. Data suggest that the major role of adenosine deaminases in various taxa is the protection of tissues against increased levels of adenosine and deoxyadenosine. This review also discusses potential roles of adenosine deaminases in Drosophila metamorphosis and the employment of a Drosophila model to study the cell-specific toxicity of elevated nucleoside levels.

Two STR loci polymorphisms of adenosine deaminase gene in Japanese population

Polymorphism of two tetranucleotide tandem repeat loci in the adenosine deaminase (ADA) gene was studied in a Japanese population. A TAAA repeat at approximately 1100 nucleotide 5' to the ADA transcription initiation site, and a TTTA repeat within intron 3 of the ADA gene were characterized using the polymerase chain reaction (PCR) and sequence analysis. Among the 235 individuals studied, seventeen genotypes at the ADA-TAAA locus and ten genotypes at the ADA-TTTA locus were identified, yielding discrimination potentials of 0.90 and 0.66, respectively. The observed and expected genotype values are consistent with Hardy-Weinberg equilibrium. The allele frequencies in the Japanese population were compared with the reported values for other populations. At the ADA-TAAA locus, there were significant differences between the Japanese population and an American Caucasian sample. At the ADA-TTTA locus, no significant differences were observed between Japanese and Chinese or between Japanese and Basques, but significant differences were found between our Japanese population and Italians and Mossi.

Identification of ephrin-A3 and novel genes specific to the midbrain-MHB in embryonic zebrafish by ordered differential display

Development of the tectum and the cerebellum is induced by a reciprocal inductive signaling between their respective primordia, the midbrain and the midbrain/hindbrain boundary (MHB). We set out to identify molecules that function in and downstream of this reciprocal signaling. Overexpression of LIM domain of the transcription factor Islet-3 (LIM(Isl-3)) leads to inhibition of this reciprocal signaling and to resultant defects in tectal and cerebellar development. We therefore searched for genes that may be either up- or down-regulated by overexpression of LIM(Isl-3) by comparing the gene expression profiles in the midbrain and the MHB of normal embryos and embryos in which Islet-3 function was repressed, using a combination of ordered differential display and whole-mount in situ hybridization. Among genes identified in this search, two cDNA fragments encoded Wnt1 and FGF8, which are already known to be essential for the reciprocal signaling between the midbrain and the MHB, confirming the effectiveness of our strategy. We identified four other partial cDNA clones that were specifically expressed around the MHB, ten cDNAs specifically expressed in the tectum, and three cDNAs expressed in neural crest cells including those derived from the midbrain level. The ephrin-A3 gene was specifically expressed in posterior tectum in a gradient that decreased anteriorly. Although ephrin-A2 and ephrin-A5 have been reported to be expressed in the corresponding region in mouse embryos, the superior/inferior colliculi, mouse ephrin-A3 is not expressed prominently in this region, suggesting that the role of ephrin-A3 in brain development may have been altered in the process of brain evolution.

Cloning of human neuronatin gene and its localization to chromosome-20q 11.2-12: the deduced protein is a novel "proteolipid'

Human brain development is a continuum governed by differential gene expression. Therefore, we proceeded to identify genes selectively expressed in the developing brain. Using differential display and library screening, a novel rat cDNA, neuronatin, was identified and used to screen a human fetal brain cDNA library. Human neuronatin cDNA was isolated and sequenced. The cDNA was 1159 bp long and corresponded in size to the 1.25 kb message detected on Northern analysis. Neuronatin mRNA was selectively expressed in human brain during fetal development, but became repressed in adulthood. When studied in the rat, neuronatin mRNA first appeared at mid-gestation in association with the onset of neurogenesis, becoming most pronounced later in development when neuroepithelial proliferation and neuroblast commitment are manifest, and declined postnatally coinciding with the completion of neurogenesis. The deduced protein has two distinct domains, a hydrophobic N-terminal and basic C-terminal rich in arginine residues. Both the amino acid sequence and secondary structure of this amphipathic polypeptide exhibited homology to PMP1 and phospholamban, members of the "proteolipid' class of proteins which function as regulatory subunits of membrane channels. The neuronatin gene, 3973 bases long, contains in its 5'-flanking region a neural restrictive silencer element which may govern neuron-specific expression. Based on screening a somatic cell hybrid panel, neuronatin gene was assigned to chromosome-20. And, using deletion constructs of chromosome-20 and fluorescence in situ hybridization, neuronatin was localized to chromosome-20q11.2-12. In conclusion, neuronatin is a novel human gene that is developmentally regulated and expressed in the brain. The deduced protein is a proteolipid that may function as a unique regulator of ion channels during brain development. The definitive localization of neuronatin to human chromosome 20q11.2-12 provides the basis to investigate this gene as a candidate in neuro-developmental diseases that may also map to this region.

The gene and pseudogenes of rat S-adenosyl-L-homocysteine hydrolase

Two rat liver genomic DNA libraries constructed in lambda DASH and lambda Charon 4A were screened for sequences with similarity to S-adenosyl-L-homocysteine (AdoHcy) hydrolase cDNA. Of 36 clones purified, two contained the AdoHcy hydrolase gene sequence and 34 contained pseudogene sequences. The AdoHcy hydrolase gene, which has been sequenced in its entirety, spans approximately 15 kb and consists of 10 exons. Primer extension and S1 experiments show that transcription is initiated from two major initiation sites located at positions -63 and -62 from the starting codon and from several minor sites. The promoter region is located in a CpG island, sequence TATTTAAA is present 23 bases upstream from the transcription start site, and an inverted CCAAT box is located 285 bp upstream from the transcription start site. Other potential transcription-factor binding sites including SP1, AP-2, GRE and Oct-1 sites were identified in the 5'-flanking region. Several different processed pseudogenes were found and analyzed.

Mapping of the structural gene for S-adenosyl homocysteine hydrolase to mouse chromosome 2, and related sequences to chromosomes 8 and X

Comparative mapping studies in human and mouse have shown that, to date, human Chromosome (Chr) 20 is completely syntenic with distal mouse Chr 2. The structural locus for S-adenosyl-L-homocysteine hydrolase (EC 3.3.1.1) in human, AHCY, maps to 20 qter-->q13.1, and we report here that the homologous locus in the mouse, Ahcy, maps to distal mouse Chr 2 with gene order Pcna-Ahcy-Ada. Analysis of 123 progeny of an interspecific backcross between a laboratory stock, AN, and Mus spretus using a rat cDNA probe revealed the presence of at least two other Ahcy-related sequences segregating independently in the mouse genome. One, Ahcy-rs1, was mapped to Chr 8 in the BXH recombinant inbred strains, and the other, Ahcy-rs2, shows a pattern of inheritance consistent with X-linkage.

Physical localization of chromosome 20 markers using somatic cell hybrid cell lines and fluorescence in situ hybridization

A panel of somatic cell hybrid cell lines containing different parts of human chromosome 20 and fluorescence in situ hybridization have been used to physically localize markers to human chromosome 20. Through these complementary approaches and genetic linkage analysis, D20S16, which is closely linked to the maturity onset diabetes of the young (MODY) locus, was mapped to band 20q12 --> q13.1. The gene for growth hormone-releasing factor (GHRF) was physically mapped and reassigned to 20q11, suggesting that GHRF plays no direct role in MODY. In addition, the genes for the chromosome 20-linked glycogen phosphorylase (GYPB) and the bone morphogenetic protein (BMP2A) have been assigned to chromosome 20p, and the interleukin-6-dependent DNA-binding protein (TCF5) has been assigned to 20q12 --> q13 by hybridization to genomic DNA from the panel of somatic cell hybrid cell lines. These approaches are useful for rapid localization of candidate genes for MODY and other DNA markers mapped to chromosome 20.

Kinetic properties of the common electrophoretic variants of human S-adenosylhomocysteine hydrolase (AHCY): the effect of four nucleoside analogue inhibitors

Red blood cell S-adenosylhomocysteine hydrolase (AHCY) from individuals of 1, 2-1 and 3-1 phenotypes was partially purified and Km and Vmax determined in the absence and in the presence of the following inhibitors: 3-deaza-adenosine (DZA), 3-deaza-aristeromycin (DZAry), 2-chloro adenosine (2-Cl-ado) and purine riboside (or nebularine). The three phenotypes 1, 2-1, 3-1 showed similar Km (32.58, 39.22 and 34.84 microM respectively), but the ratio Km/Vmax was statistically different. DZA and DZAry appeared to be strong competitive inhibitors. The AHCY 1 phenotype was more resistant to their action, while the 3-1 variant was more sensitive. 2-Cl-ado and purine riboside were weaker inhibitors; the type of inhibition varied among the three phenotypes, but, again, the AHCY 1 phenotype was less sensitive than the other two.

Genomic organization and molecular genetics of the agouti locus in the mouse

The agouti locus regulates a switch in pigment synthesis by hair bulb melanocytes between eumelanosomes and phaeomelanosomes. The agouti locus appears to encode a trans-acting product that acts within the hair follicle to direct the pigment synthesis of melanocytes. In addition to coat color, several agouti mutations affect development, obesity, and susceptibility to neoplasms. The genomic organization of the agouti region suggests that there are three functional units involved in prenatal lethality flanking the agouti coat color locus. Molecular probes for the agouti region are needed to identify and study the genes responsible for these pleiotropic effects. Classical genetic crosses coupled with molecular genetic analyses have been used to determine the map distance and orientation of molecular loci in the agouti region of mouse chromosome 2. The proximity of some of these molecular probes to the agouti region enables the use of molecular markers designed to clone sequences from the agouti locus. Pulsed-field gel electrophoresis is being used to establish long-range restriction maps surrounding the agouti region. Identification of DNA alterations corresponding to specific agouti mutations will enable determination of the molecular basis of agouti locus phenotypes. The mechanism by which the agouti gene product(s) tells the melanocyte what type of pigment to produce may involve cell-cell communication and signal transduction pathways. Future experiments will determine the type of protein(s) encoded by the agouti coat color locus and establish the mechanism by which these protein(s) control the nature and timing of pigment production by melanocytes in the hair follicle.

Four distinct alpha satellite subfamilies shared by human chromosomes 13, 14 and 21

We describe the characterisation of four alpha satellite sequences which are found on a subset of the human acrocentric chromosomes. Direct sequence study, and analysis of somatic cell hybrids carrying specific human chromosomes indicate a unique 'higher-order structure' for each of the four sequences, suggesting that they belong to different subfamilies of alpha DNA. Under very high stringency of Southern hybridisation conditions, all four subfamilies were detected on chromosomes 13, 14 and 21, with 13 and 21 showing a slightly greater sequence homology in comparison to chromosome 14. None of these subfamilies were detected on chromosomes 15 and 22. In addition, we report preliminary evidence for a new alphoid subfamily that is specific for human chromosome 14. These results, together with those of earlier published work, indicate that the centromeres of the five acrocentric chromosomes are characterised by a number of clearly defined alphoid subfamilies or microdomains (with at least 5, 7, 3, 5 and 2 different ones on chromosomes 13, 14, 15, 21 and 22, respectively). These microdomains must impose a relatively stringent subregional pairing of the centromeres of two homologous chromosomes. The different alphoid subfamilies reported should serve as useful markers to allow further 'dissection' of the structure of the human centromere as well as the investigation of how the different nonhomologous chromosomes may interact in the aetiology of aberrations involving these chromosomes.

Paradoxical expression of adenosine deaminase in T cells cultured from a patient with adenosine deaminase deficiency and combine immunodeficiency

T lymphocytes cultured from a patient (T.D.) with adenosine deaminase (ADA) deficiency expressed ADA activity in the normal range, inconsistent with her severe immunodeficiency, metabolic abnormalities, and with the absence of ADA activity in her B lymphocytes and other nucleated hematopoietic cells. ADA from T.D. T cells had normal Km, heat stability, and sensitivity to ADA inhibitors. Examination of HLA phenotype and polymorphic DNA loci indicated that T.D. was neither chimeric nor a genetic mosaic. Amplified and subcloned ADA cDNA from ADA+ T.D. T cells was shown by allele-specific oligonucleotide hybridization to possess the same mutations (Arg101----Trp, Arg211----His) previously found in the ADA-T.D. B cell line GM 2606 (Akeson, A. L., D. A. Wiginton, M. R. Dusing, J. C. States, and J. J. Hutton. 1988. J. Biol. Chem. 263:16291-16296). Our findings suggest that one of these mutant alleles can be expressed selectively in IL-2-dependent T cells as stable, active enzyme. Cultured T cells from other patients with the Arg211----His mutation did not express significant ADA activity, while some B cell lines from a patient with an Arg101----Gln mutation have been found to express normal ADA activity. We speculate that Arg101 may be at a site that determines degradation of ADA by a protease that is under negative control by IL-2 in T cells, and is variably expressed in B cells. Il-2 might increase ADA expression in T cells of patients who possess mutations of Arg101.

A molecular genetic linkage map of mouse chromosome 2

Interspecific backcross mice were used to create a molecular genetic linkage map of chromosome 2. Genomic DNAs from N2 progeny were subjected to Southern blot analysis using molecular probes that identified the Abl, Acra, Ass, C5, Cas-1, Fshb, Gcg, Hox-5.1, Jgf-1, Kras-3, Ltk, Pax-1, Prn-p, and Spna-2 loci; these loci were added to the 11 loci previously mapped to the distal region of chromosome 2 in the same interspecific backcross to generate a composite multilocus linkage map. Several loci mapped near, and may be the same as, known mutations. Comparisons between the mouse and the human genomes indicate that mouse chromosome 2 contains regions homologous to at least six human chromosomes. Mouse models for human diseases are discussed.

Expression of human adenosine deaminase in murine hematopoietic cells

Multiple replication-defective retrovirus vectors were tested for their ability to transfer and express human adenosine deaminase in vitro and in vivo in a mouse bone marrow transplantation model. High-titer virus production was obtained from vectors by using both a retrovirus long terminal repeat promoter and internal transcriptional units with human c-fos and herpes virus thymidine kinase promoters. After infection of primary murine bone marrow with one of these vectors, human adenosine deaminase was detected in 60 to 85% of spleen colony-forming units and in the blood of 14 of 14 syngeneic marrow transplant recipients. This system offers the opportunity to assess methods for increasing efficiency of gene transfer, for regulation of expression of foreign genes in hematopoietic progenitors, and for long-term measurement of the stability of expression in these cells.

Isozyme and DNA analysis of human S-adenosyl-L-homocysteine hydrolase (AHCY)

Erythrocyte and tissue isozymes of human AHCY have been studied by starch gel electrophoresis, cellulose acetate electrophoresis, isoelectric focusing and Na dodecyl sulphate electrophoresis. The same isozyme was observed in all the tissues studied, suggesting that human AHCY is encoded by a single structural locus. Two variant alleles were identified in erythrocyte AHCY using starch gel electrophoresis in a sample of 166 unrelated individuals from the British population. The gene frequencies were 0.024 for AHCY*2 and 0.006 for AHCY*3. The variant isozyme patterns could not be distinguished by isoelectric focusing. Using the homologous rat cDNA AHCY probe, human AHCY cDNA recombinants were isolated from a placental cDNA library. The human and rat sequences show considerable homology in the coding region of the gene and also, but to a lesser extent, in the distal part of the 3' untranslated region. Preliminary observations suggest the occurrence of a high frequency PvuII site RFLP identified with the human AHCY probe.

Sequence of full length cDNA for human S-adenosylhomocysteine hydrolase

Two cDNA clones for human S-adenosylhomocysteine hydrolase isolated from a placental cDNA library were sequenced. Each contained a sequence of 1299 nucleotides encoding a 432 amino-acid protein of MW 47,660. Clone 16-1 contained 47 nucleotides 5' of the coding region, and a 780 nucleotide 3' flanking region terminating in a poly A tail. In addition, a 101 nucleotide unprocessed intron interrupted the coding sequence at nucleotide 854 (second base of codon 285). Clone 20-1 contained 43 nucleotides 5' and 742 nucleotides 3' flanking the uninterrupted coding region. Besides the intron, the clones differed in one position of the coding sequence and at two positions of the 3' non-coding region. The cDNAs for human and rat S-adenosylhomocysteine hydrolase were identical at 91.5% of positions in the coding sequence and showed 70% homology in the 3' non-coding regions. Human and rat S-adenosyl-homocysteine hydrolases are identical at 97% of amino-acid residues, and the Dictyostelium and human enzymes at 75%.

The map of chromosome 20

The number of gene assignments to human chromosome 20 has increased slowly until recently. Only seven genes and one fragile site were confirmed assignments to chromosome 20 at the Ninth Human Gene Mapping Workshop in September 1987 (HGM9). One fragile site, 13 additional genes, and 10 DNA sequences that identify restriction fragment length polymorphisms (RFLPs), however, were provisionally added to the map at HGM9. Five mutated genes on chromosome 20 have a relation to disease: a mutation in the adenosine deaminase gene results in a deficiency of the enzyme and severe combined immune deficiency; mutations in the gene for the growth hormone releasing factor result in some forms of dwarfism; mutations in the closely linked genes for the hormones arginine vasopressin and oxytocin and their neurophysins are probably responsible for some diabetes insipidus; and mutations in the gene that regulates both alpha-neuraminidase and beta-galactosidase activities determine galactosialidosis. The gene for the prion protein is on chromosome 20; it is related to the infectious agent of kuru, Creutzfeld-Jacob disease, and Gertsmann-Straussler syndrome, although the nature of the relationship is not completely understood. Two genes that code for tyrosine kinases are on the chromosome, SRC1 the proto-oncogene and a gene (HCK) coding for haemopoietic kinase (an src-like kinase), but no direct relation to cancer has been shown for either of these kinases. The significance of non-random loss of chromosome 20 in the malignant diseases non-lymphocytic leukaemia and polycythaemia vera is not understood. Twenty-four additional loci are assigned to the chromosome: five genes that code for binding proteins, one for a light chain of ferritin, genes for three enzymes (inosine triphosphatase, s-adenosylhomocysteine hydrolase, and sterol delta 24-reductase), one for each of a secretory protein and an opiate neuropeptide, a cell surface antigen, two fragile sites, and 10 DNA sequences (one satellite and nine unique) that detect RFLPs.

Expression of human adenosine deaminase in murine hematopoietic cells

Multiple replication-defective retrovirus vectors were tested for their ability to transfer and express human adenosine deaminase in vitro and in vivo in a mouse bone marrow transplantation model. High-titer virus production was obtained from vectors by using both a retrovirus long terminal repeat promoter and internal transcriptional units with human c-fos and herpes virus thymidine kinase promoters. After infection of primary murine bone marrow with one of these vectors, human adenosine deaminase was detected in 60 to 85% of spleen colony-forming units and in the blood of 14 of 14 syngeneic marrow transplant recipients. This system offers the opportunity to assess methods for increasing efficiency of gene transfer, for regulation of expression of foreign genes in hematopoietic progenitors, and for long-term measurement of the stability of expression in these cells.

Family and population studies of SAHH and ADA polymorphisms. A possible pitfall in the ascertainment of SAHH electrophoretic phenotypes

Typing of both SAHH and ADA red cell electrophoretic patterns was carried out among the members of about 80 families from Latium (Central Italy) and in a random sample of about 350 individuals from two Italian regions, Latium and Sardinia. 1. The SAHH1 enzyme product provided another interesting example of a change in the electrophoretic pattern brought about by the haemolysate ageing. In vitro storage of SAHH 1 red cell lysates leads to the production of a pattern similar to that expected from a heterozygote SAHH 2-1. This change has been shown to be abolished by pretreating the sample with mercaptoethanol. The results indicate that the systematic use of sulphydril reducing agents can provide a more reliable means of analysing the SAHH polymorphism if differently stored samples are to be compared by starch gel electrophoresis. 2. Evidence against complete linkage of the SAHH and ADA loci has been obtained from two informative SAHH/ADA matings encountered in this study. 3. The SAHH allele frequencies observed in the two samples analysed were: SAHH1 = 0.969, SAHH2 = 0.024, SAHH3 = 0.007 (Latium) and SAHH1 = 0.973, SAHH2 = 0.011, SAHH3 = 0.016 (Sardinia). 4. The ADA2 allele frequency estimates were: 0.083 (Latium) and 0.059 (Sardinia). These figures are almost identical to those already reported for the same two regions.

Assignment of the human and mouse prion protein genes to homologous chromosomes

Purified preparations of scrapie prions contain one major macromolecule, designated prion protein (PrP). Genes encoding PrP are found in normal animals and humans but not within the infectious particles. The PrP gene was assigned to human chromosome 20 and the corresponding mouse chromosome 2 using somatic cell hybrids. In situ hybridization studies mapped the human PrP gene to band 20p12----pter. Our results should lead to studies of genetic loci syntenic with the PrP gene, which may play a role in the pathogenesis of prion diseases or other degenerative neurologic disorders.

Assignment of a human beta-crystallin gene to 17cen-q23

The gene map assignment of a human beta-crystallin gene to 17cen-q23 has been made using a bovine probe in the study of human-mouse and human-Chinese hamster somatic cell hybrids containing parts of human chromosome 17.

Covalent labelling of ligand binding sites of human placental S-adenosylhomocysteine hydrolase with 8-azido derivatives of adenosine and cyclic AMP

S-Adenosylhomocysteine hydrolase (AdoHcyase) has previously been identified as a cytoplasmic adenosine and cyclic AMP binding protein. In order to examine the relationship between the adenosine and cyclic AMP binding sites on this enzyme we have explored the use of 8-azido analogues of adenosine and cyclic AMP as photoaffinity reagents for covalently labelling AdoHcyase purified from human placenta. 8-Azidoadenosine (8-N3-Ado), like adenosine, inactivated AdoHcyase, and the rate of inactivation was greatly increased by periodate oxidation. In addition, 8-N3-Ado was found to participate in the first step in the catalytic mechanism for AdoHcyase, resulting in conversion of enzyme-bound NAD+ to NADH, although it was not a substrate for the full enzyme-catalysed reaction. Radioactively labelled 8-N3-Ado, its periodate-oxidized derivative and 8-azidoadenosine 3', 5'-phosphate (8-N3-cAMP) bound specifically to adenosine binding sites on AdoHcyase and, after irradiation, became covalently linked to the enzyme. Photoaffinity-labelled enzyme could be precipitated by monoclonal antibody to human AdoHcyase. Two observations suggested that cyclic AMP and adenosine bind to the same sites on AdoHcyase. First cyclic AMP and adenosine each blocked binding of both radioactively labelled 8-N3-Ado and 8-N3-cAMP, and second, digestion with V8 proteinase generated identical patterns of peptides from AdoHcyase that had been photolabelled with [32P]8-N3-cAMP and [3H]8-N3-Ado. Binding sites for cyclic AMP on AdoHcyase were found to differ functionally and structurally from cyclic AMP binding sites on the R1 regulatory subunit of cyclic AMP-dependent protein kinase.

A human c-src gene resides on the proximal long arm of chromosome 20 (cen----q131)

A molecular clone of v-src, the oncogene of Rous sarcoma virus, was used to detect and regionally localize a human c-src proto-oncogene on chromosome #20. The human c-src gene, detected as either a 28-kbp EcoRI DNA fragment or as a 15.4-kbp BglII DNA fragment, was localized to 20 cen----q131 by filter hybridization analysis of DNAs from human-rodent somatic cell hybrids. The results indicate that c-src is on the same chromosome arm as aberrations associated with myeloproliferative disease, although the possible involvement of c-src in these aberrations is unknown.

S-Adenosylhomocysteine hydrolase from human placenta. Affinity purification and characterization

S-Adenosylhomocysteine hydrolase (EC 3.3.1.1) was purified to homogeneity from human placenta by using S-adenosylhomocysteine-agarose affinity chromatography. The enzyme is a tetramer with a native Mr of 189 000 and subunit Mr of 47 000-48 000; there were nine cysteine residues per subunit and no disulphide bonds. The pI was 5.7. H.p.l.c. analysis revealed that the enzyme contained four molecules of tightly bound cofactor (NAD) per tetramer, of which 10-50% was in the reduced form. The enzyme had four binding sites per tetramer for adenosine, of which 10-35% were found to be occupied. Two types of adenosine-binding sites could be distinguished on the basis of differences in rates of dissociation of the enzyme-adenosine complex, and by examining binding of adenosine at 0 degree C and 37 degrees C. The enzyme catalysed the interconversion of adenosine and 4',5'-dehydroadenosine; the equilibrium constant for this reaction was 2.1 and favoured 4',5'-dehydroadenosine formation. Variability in the specific activity of preparations of S-adenosylhomocysteine hydrolase was related to the NAD+/NADH ratio of the preparation. The capacity to bind radioactively labelled adenosine depended on the adenosine content of the purified enzyme. The rate of adenosine binding and the sensitivity of S-adenosylhomocysteine hydrolase to inactivation by adenosine were both diminished in the absence of dithiothreitol.

Prenatal diagnosis of a true mosaic trisomy 20 substantiated by demonstration of a gene dosage effect for adenosine deaminase (ADA)

Fibroblasts from a fetus with the prenatal diagnosis of mosaic trisomy 20 were cloned by dilution plating. Adenosine deaminase (ADA), a biochemical marker for chromosome 20, was assayed in trisomic clones and normal clones as control. The cytogenetic diagnosis was substantiated by demonstration of a triplex gene dosage effect for ADA in the trisomic cells.

Gene frequencies of S-adenosylhomocysteine hydrolase (SAHH) in a Japanese population

Genetic polymorphism of S-adenosylhomocysteine hydrolase (SAHH) was investigated in a total of 214 red blood cell samples from unrelated Japanese using the starch gel electrophoresis and the enzyme-specific staining procedures. Three common phenotypes were observed which corresponded to SAHH 1, SAHH 2-1, and SAHH 2, controlled by two alleles, SAHH*1 and SAHH*2. The estimated gene frequencies of SAHH*1 and SAHH*2 in Japanese were 0.953 and 0.047, respectively. This result was not different from European samples reported by Bissbort et al. (1983).