Mannosidosis: assignment of the lysosomal alpha-mannosidase B gene to chromosome 19 in man

Alpha-Mannosidosis: Therapeutic Strategies

Alpha-mannosidosis (α-mannosidosis) is a rare lysosomal storage disorder with an autosomal recessive inheritance caused by mutations in the gene encoding for the lysosomal α-d-mannosidase. So far, 155 variants from 191 patients have been identified and in part characterized at the biochemical level. Similarly to other lysosomal storage diseases, there is no relationship between genotype and phenotype in alpha-mannosidosis. Enzyme replacement therapy is at the moment the most effective therapy for lysosomal storage disease, including alpha-mannosidosis. In this review, the genetic of alpha-mannosidosis has been described together with the results so far obtained by two different therapeutic strategies: bone marrow transplantation and enzyme replacement therapy. The primary indication to offer hematopoietic stem cell transplantation in patients affected by alpha-mannosidosis is preservation of neurocognitive function and prevention of early death. The results obtained from a Phase I⁻II study and a Phase III study provide evidence of the positive clinical effect of the recombinant enzyme on patients with alpha-mannosidosis.

Isolation and characterization of the gene encoding the mouse broad specificity lysosomal alpha-mannosidase1

A genomic clone encoding the mouse lysosomal alpha-mannosidases was isolated and the gene was found to be encoded by 24 exons spanning approximately 14.5 kb of genomic DNA. The intron-exon boundaries were conserved between the mouse, human, and bovine lysosomal alpha-mannosidase genes as well as being partially conserved in several other species. In order to define the promoter of the mouse mannosidase gene, >1 kb of DNA sequence was obtained upstream from the respective initiation codon. The transcription start site was identified by a 5'-RACE procedure and putative promoter elements were identified by expression of promoter/reporter constructs. Fluorescence in situ hybridization analysis using the mouse and human mannosidase genomic clones as probes, localized the mouse gene to chromosome 8, at band position 8C2, and the human gene to chromosome 19p13.2, a region syntenic to the lysosomal mannosidase gene on mouse chromosome 8.

alpha-Mannosidosis: functional cloning of the lysosomal alpha-mannosidase cDNA and identification of a mutation in two affected siblings

a-Mannosidosis (MIM 248500) is an autosomal recessive lysosomal storage disorder resulting from deficient activity of lysosomal alpha-mannosidase (LAMAN) (EC 3.2.1.24). The disease is characterized by massive intracellular accumulation of mannose-rich oligosaccharides with resulting mental retardation, hearing loss, immune deficiency and skeletal changes. We report here the purification and characterization of human placenta LAMAN. The enzyme is synthesized as a single-chain precursor which is processed into three glycopeptides of 70, 42 and 15 kDa. The 70 kDa peptide is further partially proteolysed into three more peptides that are joined by disulfide bridges. The laman cDNA sequence was assembled from overlapping fragments obtained by PCR on human fibroblast and human lung cDNA. The deduced amino acid sequence contains a putative signal peptide of 48 amino acids followed by a polypeptide sequence of 962 amino acids. Northern blot analyses revealed a single transcript of approximately 3.5 kb present in all tissues examined but at varying levels. Two affected siblings of Palestinian origin were homozygous for a mutation that causes a His-->Leu replacement at a position which is conserved among class 2 alpha-mannosidases from several species.

Cloning, expression, purification, and characterization of the human broad specificity lysosomal acid alpha-mannosidase

We have cloned and expressed two cDNAs encoding the human lysosomal alpha-mannosidase (EC 3.2.1.24) by RT-PCR of human spleen mRNA. This enzyme is required for the degradation of N-linked carbohydrates during glycoprotein catabolism in eucaryotic cells. The shorter of the two cDNAs (3 kilobases (kb)) was found to encode an open reading frame of 2964 base pairs and, when expressed in Pichia pastoris, was found to encode an enzyme that could cleave high mannose oligosaccharides, oligosaccharides isolated from alpha-mannosidosis fibroblasts, and p-nitrophenyl-alpha-D-mannopyranoside substrates. In addition, the Pichia-expressed enzyme was inhibited by swainsonine, and had a pH optimum, Km, and Vmax characteristic of the enzyme purified previously from human liver. The second, larger RT-PCR product (3.6 kb) was found to contain an insertion and a deletion relative to the 3-kb spleen amplimer and encoded a truncated coding region, indicating that it resulted from alternate transcript splicing. No alpha-mannosidase activity could be detected in Pichia transformants containing this coding region, indicating that it did not encode a functional enzyme. Antiserum raised to the recombinant product of the 3-kb alpha-mannosidase cDNA immunoprecipitated lysosomal alpha-mannosidase activity from human fibroblast extracts. Northern blots identified a 3-kb RNA transcript in all human tissues tested, including alpha-mannosidosis fibroblasts, while minor transcripts of 3.6 kb were also present in several adult tissues. Human chromosome mapping of the mannosidase gene confirmed that the functional gene maps to the MANB locus on chromosome 19. Sequence comparisons were made to previously published human cDNA sequences encoding a putative lysosomal alpha-mannosidase (Nebes, V. L., and Schmidt, M. C. (1994) Biochem. Biophys. Res. Commun. 200, 239-245) and several differences were found relative to the functional lysosomal alpha-mannosidase encoded by the 3-kb spleen cDNA.

The core-specific lysosomal alpha(1-6)-mannosidase activity depends on aspartamidohydrolase activity

The substrate specificity of the core-specific rat liver lysosomal alpha(1-6)-mannosidase was investigated using mannosylated oligosaccharides and glycoasparagines. Hydrolysis of Man(alpha 1-6) linkage hydrolysis was demonstrated to follow the action of endoglycosidases, namely aspartyl-N-acetyl-beta-D-glucosaminidase and endo-N-acetyl-beta-D-glucosaminidase. The results are discussed with respect to the nature of the carbohydrate materials stored in the tissues and excreted in the urine from patients suffering from aspartylglucosaminuria and fucosidosis.

Purification and comparison of the structures of human liver acidic alpha-D-mannosidases A and B

Human liver alpha-D-mannosidases A and B were purified 11 500-fold and 2000-fold respectively. Both showed microheterogeneity when analysed by isoelectric focusing. Alpha-D-Mannosidases A and B are immunologically identical but differ in their range of pI values, molecular masses, uptake into fibroblasts and subunit compositions. Alpha-D-Mannosidase A consists of equimolar proportions of subunits of molecular masses 62 kDa and 26 kDa, which are linked by disulphide bridges in the intact enzyme. Alpha-D-Mannosidase B also contains a small subunit, of molecular mass 26 kDa, and a variable mixture of larger subunits, of molecular masses 58 kDa and 62 kDa. The 62 kDa and 58 kDa subunits, but not the 26 kDa one, contain concanavalin A-recognizing glycans. The 58 kDa subunit has a lower pI, contains less high-mannose glycans but probably contains more mannose 6-phosphate than the 62 kDa subunit. It is postulated that the differences in structure and properties of alpha-D-mannosidases A and B are due to differences in the state of processing of the large subunit. This suggestion is consistent with a single locus on chromosome 19 for lysosomal alpha-D-mannosidase.

Transformation associated p53 protein is encoded by a gene on human chromosome 17

The human gene for the transformation-associated p53 phosphoprotein (P53) was assigned to the short arm of chromosome 17 using human-rodent somatic cell hybrids and Southern filter hybridization of cell hybrid DNA. The filters were hybridized to radiolabeled DNA from a genomic clone which contained P53 nucleotide sequences. Hybridization of the probe to a 2.5-kb human DNA fragment in HindIII-digested DNA was used to identify the human P53 gene.

Further regional localization of the genes for human acid alpha glucosidase (GAA), peptidase D (PEPD), and alpha mannosidase B (MANB) by somatic cell hybridization

We have further regionally localized the gene for human acid alpha glucosidase (GAA) to 17q21----q23 by examination of hybrid clones derived from a fusion between human fibroblasts carrying a 17/19 balanced translocation (17pter----17q23::19p13.3----19pter; 19qter----p13.3::17q23----17qter) and a mouse line deficient in thymidine kinase. These hybrids were constantly maintained in HAT selective media in order to select for the presence of the human thymidine kinase gene on the intact chromosome 17 (17q21-q22) or the 17/19 (17pter----17q23::19p13.3----19pter) translocation chromosome. We detected human GAA by rocket immunoelectrophoresis, using a human specific heterologous antibody raised against human acid alpha glucosidase (GAA) (Honig et al. 1984). Three secondary clones, which contained the 17/19 translocation and no intact chromosome 17 or 19, were still positive for GAA. Two of these secondary clones contained the distal portion of the 17/19 translocation chromosome, with a break in the band 17q21 (probably at 17q21.2), attached to a mouse chromosome. Combined with earlier results (Weil et al. 1979; Nickel et al. 1982; Honig et al. 1984), the gene for GAA can be assigned to 17q21.2----17q23. Additionally, these clones were negative for human peptidase D (PEPD), alpha mannosidase B (MANB), and phosphohexose isomerase (PHI). Combined with previous results (Ingram et al. 1977; Bruns et al. 1979), these results exclude the genes for PEPD and MANB from 19pter----19p13.3 and confirm the exclusion of the gene for PHI from this segment of chromosome 19 (Wilson et al. 1984; Ingram et al. 1977).

Chromosomal assignments of human genes for serine proteases trypsin, chymotrypsin B, and elastase

The genes for the serine proteases trypsin, chymotrypsin B, and elastase were chromosomally assigned in man using cDNA probes that have been isolated from a rat pancreatic cDNA library. DNA from human X rodent somatic cell hybrids was cleaved with BamHI or EcoRI and analyzed by Southern filter hybridization methods for the segregation of the genes for trypsin-1 (TRY1), chymotrypsin B (CTRB), and elastase-1 (ELA1). TRY1 was assigned to human chromosome 7q22----qter, CTRB to chromosome 16, and ELA1 to chromosome 12. Although the three genes are members of the same gene family, they are dispersed over different chromosomes.

Two nonallelic tRNAiMet genes are located in the p23 leads to q12 region of human chromosome 6

Two nonallelic human tRNAiMet genes were assigned to chromosome 6 by filter hybridization of DNA from human-rodent somatic cell hybrids by using probes containing unique sequences from the regions flanking each tRNAiMet gene. These unique sequence probes thus allowed each tRNAiMet gene to be analyzed individually in cell hybrids. Both tRNAiMet genes segregated in the hybrid cells with the chromosome 6 enzyme markers, soluble malic enzyme and the mitochondrial form of superoxide dismutase, and also with a karyotypically normal chromosome 6. By using hybrid clones containing translocations that divide chromosome 6 into five segments, both tRNAiMet genes were assigned to the p23 leads to q12 region. These results raise the possibility that other tRNAiMet genes may be syntenic with the two described in this study and illustrate the utility of using unique flanking sequences to identify members of a multigene family.

Genetic heterogeneity of I-cell disease is demonstrated by complementation of lysosomal enzyme processing mutants

I-cell disease (mucolipidosis II) is a fatal childhood disorder affecting the expression of multiple lysosomal acid hydrolases. The disorder is characterized by clinical and biochemical heterogeneity which may reflect different mutants with a similar phenotype. Genetic complementation studies demonstrating genetic heterogeneity within this disorder are described utilizing cultured fibroblasts from 11 different patients. Fibroblasts from I-cell disease (ICD) and from five different lysosomal storage diseases with single structural gene enzyme deficiencies were fused in different combinations, and fractions enriched for multinucleated heterokaryons were isolated and tested for acid hydrolase activity and electrophoretic mobility. In fusions of ICD fibroblasts and various single lysosomal enzyme-deficient fibroblasts, the activity of the deficient enzyme and of the other ICD hydrolases were restored, demonstrating that ICD is not a lysosomal enzyme structural gene defect and that the ICD defect, and not just the single enzyme deficiency, is corrected. In fusions involving only I-cell fibroblasts, at least two complementation groups were identified by the recovery of activities of all lysosomal enzymes tested in heterokaryons. These results demonstrate the existence of genetic heterogeneity within the disorder and suggest that different mutations can result in the I-cell clinical and biochemical phenotype. The data support an altered post-translational processing of lysosomal enzymes as the cause of ICD and suggest that at least two genes participate in this pathway.

Coronavirus 229E susceptibility in man-mouse hybrids is located on human chromosome 15

Human coronavirus 229E, n enveloped, RNA-containing virus, causes respiratory illness in man and is serologically related to murine coronavirus JHM, which causes acute and chronic demyelination in rodents. 229E displays a species-specific host range restriction whose genetic basis was studied in human-mouse hybrids. 229E replicated in human WI-38 cells but not in three mouse cell lines tested (RAG, LM/TK-, and A9). Human coronavirus sensitivity (HCVS) was expressed as a dominant phenotype in hybrids, indicating that mouse cells do not actively suppress 229E replication. HCVS segregated concordantly with the human chromosome 15 enzyme markers mannose phosphate isomerase (MPI) and the muscle form of pyruvate kinase (PKM2), and analysis of hybrids containing an X/15 translocation [t(X;15)(p11;q11)] localized HCVS to the q11 leads to qter region of chromosome 15. HCVS might code for a specific surface receptor, allowing 229E to be absorbed to and received within the host cell.

Assignment of the glyoxalase II gene (HAGH) to human chromosome 16

The human and rodent forms of glyoxalase II (Hydroxyacylglutathione hydrolase, HAGH) can readily be separated by starch gel electrophoretic procedures. Fifty-one human-rodent somatic cell hybrid clones were examined for their human HAGH and for human enzyme markers whose genes are encoded on each autosome and the X chromosome. Sixteen clones were also examined for their human karyotypes. Human glyoxalase II segregated only with chromosome 16, demonstrating that the gene is located on this chromosome.

The prolactin gene is located on chromosome 6 in humans

The gene for prolactin has been located on chromosome 6 in humans. DNA fragments of 4.8 and 4.0 kilobases containing prolactin gene sequences were identified in human genomic DNA, whereas DNA fragments of 7.4, 3.6, and 3.3 kilobases containing prolactin gene sequences were found in mouse cells. In somatic cell hybrids of human and mouse cells the 7.4-, 3.6-, and 3.3-kilobase mouse fragments were always present, whereas the 4.8- and 4.0-kilobase human fragments were only present when human chromosome 6 was also present. We conclude that the prolactin gene resides on chromosome 6, a different location from those of the genes for the related hormones chorionic somatomammotropin and growth hormone.

Expression of H1 histone genes in mouse-human somatic cell hybrids

The synthesis of H1 histones was studied in nine mouse-human somatic cell hybrid clones containing reduced numbers of human chromosomes. The entire human genome could be accounted for karyologically and by the use of functional assays for specific enzyme markers encoded by human chromosomes. Chromatographic resolution and peptide mapping of species-specific H1 histones failed to reveal human H1 histones to a level of about 1% of total in the nine clones. In addition to the species-specific extinction of human H1 histones, effects were seen on the quantity of mouse H1 histone subtypes produced in four of the nine clones. The remaining five clones produced H1 histones qualitatively and quantitatively identical with those of the mouse parent, which was common to all nine clones. The results suggest at least two levels of control for H1 histone gene expression.

DNA-mediated cotransfer of unlinked mammalian cell markers into mouse L cells

Purified DNA from three different types of mammalian cells was precipitated with calcium phosphate and added to mouse L cells deficient in thymidine kinase (TK). Donor DNA was prepared from three cell lines: (a) mouse cells transfected with UV-inactivated herpes simplex virus (HSV) type 1, or a purified fragment of HSV carrying the TK gene (b) human HeLa cells, and (c( CHO, a cell line derived from Chinese hamster ovaries. Several hypoxanthine-aminopterin-thymidine resistant colonies were isolated from each experiment. The origin of the TK that is expressed in these cells was studied by polyacrylamide gel electrohporesis, isoelectric focusing, or heat stability. The TK in all instances was of the donor origin. To determine the extent of gene transfer we have assayed the CHO and HeLa DNA transfectants for galactokinase (GALK), a marker closely linked to TK, and 25 other isozymes representing a large number of different chromosomes. No cotransfer of GALK was observed, indicating that the size of the transferred DNA segment is limited. We observed that, in one instance, esterase-D, an unlinked marker of Chinese hamster origin, was transferred along with TK. These experiments indicate that nonselected markers can be transferred by this method, although at a low efficiency.

Somatic cell genetics of adenosine deaminase expression and severe combined immunodeficiency disease in humans

The somatic cell hybrid method has been used to study the number and different types of human genes involved in the expression of adenosine deaminase (ADA; adenosine aminohydrolase, EC 3.5.4.4) in normal cells and cells from a patient with ADA-deficient severe combined immunodeficiency disease (SCID). Genetic and biochemical characterization of ADA in SCID and the ADA tissue-specific isozymes in normal human cells indicates that additional genes, besides the ADA structural gene on chromosome 20, are involved in ADA expression. Human chromosome 6 encodes a gene, ADCP-1, whose presence is necessary for the expression of an ADA-complexing protein in human-mouse somatic cell hybrids [Koch, G. & Shows, T. B. (1978) Proc. Natl. Acad. Sci. USA 75, 3876-3880]. We report the identification of a second gene, ADCP-2, on human chromosome 2, that is also involved in the expression of the ADA-complexing protein. The data indicate that these two ADCP genes must be present in the same cell for that cell to express the complexing protein. Human-mouse somatic cell hybrids, in which the human parental cells were fibroblastss from an individual with ADA-deficient SCID, also required human chromosomes 2 and 6 to express the ADA-complexing protein, indicating that neither ADCP-1 nor ADCP-2 is involved in the ADA deficiency in SCID. The SCID-mouse hybrid cells expressed no human ADA even when human chromosome 20 had been retained. The deficiency of human ADA in these hybrids maps to human chromosome 20, and therefore is not due to the repression or inhibiton of ADA or its product by unlinked genes or gene products. We propose that the expression of the polymeric ADA tissue isozymes in human cells requires at least three genes: ADA on chromosome 20, ADCP-1 on chromosome 6, and ADCP-2 on chromosome 2. A genetic scheme is presented and the different genes involved in ADA expression and their possible functions are discussed.

Human lysosomal genes: arylsulfatase A and beta-galactosidase

The segregation of human lysosomal arylsulfatase A (ARS-A) has been evaluated in 50 primary hybrid clones derived from four separate fusions involving WBCs from two unrelated individuals and three hamster cell lines. ARS-A was expressed in the hybrids as a dimeric molecule of very similar or identical subunits. The expression of this enzyme was concordant with that of mitochondrial aconitase (ACON-M), an isozyme assigned to chromosome 22, in all 50 clones and with chromosome 22 segregation in all but one of the 29 karyotyped hybrids. No other human chromosome cosegregated with 22 in these clones, suggesting that this enzyme is specified in hybrid cells by a locus (or loci) on a single chromosome. beta-Galactosidase (B-GAL) expression was analyzed with two different electrophoresis systems and with a number of cell extract preparation methods in 39 of the primary hybrid clones. The B-GAL isozyme expressed in these hybrid cells was concordant with the expression of glutathione peroxidase-1 (GPX-1), an isozyme assigned to chromosome 3, in all 39 clones and with the segregation of this chromosome in 97% of the 29 karyotyped hybrids. These observations substantiate the prior tentative assignments of an ARS-A locus to chromosome 22 and a B-GAL locus to chromosome 3 (Bruns et al., 1978a, b). The implications of the chromosome assignments of loci for 12 human lysosomal enzymes for the cellular assembly of these organelles are discussed.

Complementation of genetic disease: a velocity sedimentation procedure for the enrichment of heterokaryons

Methodology is described to enrich for heterokaryons after mammalian cell fusion. A heterogeneous cell mixture can be separated on a Sta-Put apparatus into fractions of uniform size cells by sedimentation through a 1% bovine serum albumin-5% Ficoll gradient. Unfused RAG and LM/TK- cells, differing by 10% in diameter, have been sorted by size; following fusion, larger and faster sedimenting cells were shown to be hybrids. This methodology can be utilized in genetic complementation studies of human genetic diseases where selection procedures for proliferating hybrids do not exist. When fibroblasts from individuals with Tay-Sachs disease [deficient in hexosaminidase A (HEX A-)] and Sandhoff-Jatzkewitz disease (HEX A- and HEX B-) are fused, HEX A is generated, demonstrating complementation of two different mutations. After Sta-Put fractionation, the HEX A complementation product was associated with the faster sedimenting multinuclear cells and not with the mononuclear parental cells. This methodology will facilitate detection of genetic differences in fibroblasts from related inherited disorders.

Classification of hereditary cataracts in children by linkage analysis

A total of 12-different types of hereditary cataracts have been positively assigned to the gene map. They are located on autosomes as well as on the X chromosome. This establishes several kinds of cataracts as distinct diseases caused by different mutations. In selected cases the information may be helpful for prenatal diagnosis.

Genetics of cell fusion: human chromosome 10 assignment of a gene (FUSE) that promotes polykaryocyte formation

FUSE, a human gene which promotes polykaryocyte formation, has been identified and examined in cocultivation assays between rat XC cells and human-mouse hybrids retaining different combinations of human chromosomes. Polykaryocyte formation was never detected when parental cells of hybrids were cocultivated with XC cells. Somatic genetic synteny analysis employing different hybrid sets demonstrated that FUSE was coexpressed with the chromosome 10 markers glutamate oxaloacetate transaminase (GOTs) and an external membrane protein (EMP-130). Cytogenetic analysis confirmed this assignment to human chromosome 10. FUSE was expressed by hybrids made with both human leukocytes and fibroblasts from several individuals, indicating the gene is found in different tissues and may be ubiquitous. Only XC cells were involved in polykaryocyte formation as demonstrated by 33258 Hoechst staining and the absence of heteropolymers between rat and cell hybrid multimeric enzymes. Evidence suggests that the gene FUSE produces a nondiffusible and noninfectious product that is associated with the human-mouse hybrid surface.

GM1-gangliosidosis: chromosome 3 assignment of the beta-galactosidase-A gene (beta GALA)

The structural gene (beta GALA) coding for lysosomal beta-galactosidase-A (EC 3.2.1.23) has been assigned to human chromosome 3 using man--mouse somatic cell hybrids. Human beta-galactosidase-A was identified in cell hybrids with a species-specific antiserum to human liver beta-galactosidase-A. The antiserum precipitates beta-galactosidase-A from human tissues, cultured cells, and cell hybrids, and recognizes cross-reacting material from a patient with GM1 gangliosidosis. We have analyzed 90 primary man--mouse hybrids derived from 12 separate fusion experiments utilizing cells from 9 individuals. Enzyme segregation analysis excluded all chromosomes for beta GALA assignment except chromosome 3. Concordant segregation of chromosomes and enzymes in 16 cell hybrids demonstrated assignment of beta GALA to chromosome 3; all other chromosomes were excluded. The evidence suggests that GM1 gangliosidosis is a consequence of mutation at this beta GALA locus on chromosome 3.

A new immunochemical method for the quantitative measurement of specific gene products in man-rodent somatic cell hybrids

An immunochemical method has been developed for the quantitative determination of species-specific gene products, for instance alpha-galactosidase and N-acetyl-alpha-galactosaminidase, in man-rodent hybrid cells and in the parental cell lines. Antisera raised against the purified enzymes are covalently coupled to Sepharose 4B. The gene products are specifically removed from a cell lysate by incubating with the appropriate Sepharose-coupled antiserum. After centrifugation followed by washing of the precipitated Sepharose, the enzymic activity can be quantitatively measured on the Sepharose beads. With this technique it has been demonstrated that the ability of human N-acetyl-alpha-galactosaminidase (also known as alpha-galactosidase B) to hydrolyze alpha-galactosidic linkages is lost when the enzyme is expressed in man-Chinese hamster hybrid cells.

Assignment of peptidase S (PEPS) to chromosome 4 in man using somatic cell hybrids

A starch gel electrophoretic procedure is described that resolves peptidase S (PEPS) as well as the peptidases A, B, and C in man-rodent, rodent-rodent, and primate-rodent interspecific somatic cell hybrids. The interspecific PEPS cell hybrid phenotype can be resolved into a pattern which suggests that PEPS is composed of five or six identical subunits. Results are presented supporting assignment of the PEPS locus to chromosome 4 in man using man-mouse and man-Chinese hamster somatic cell hybrids. Human genes coding for peptidases A, B, C, and D were assigned to chromosome 18, 12, 1, and 19, respectively, confirming previous assignments. These somatic cell genetic data demonstrate the independent genetic control of the several human peptidases.

A gene on human chromosome 6 functions in assembly of tissue-specific adenosine deaminase isozymes

In human tissues, adenosine deaminase (ADA) (adenosine aminohydrolase; EC 3.5.4.4) activity can be separated by gel electrophoresis into several isozymes. A structural gene (ADA) on chromosome 20 codes for the "erythrocyte" isozyme, ADA-1, which is also expressed in some nonerythroid tissues. Nonerythroid cells also differentially express five ADA "tissue isozymes" of a greater molecular weight than ADA-1. Each ADA tissue isozyme has a characteristic electrophoretic mobility and tissue distribution. It has been suggested that these ADA tissue isozymes are composed of ADA-1 and other components. We report that the expression of one of these tissue isozymes, ADA-d, is dependent upon ADA on chromosome 20 and another gene on chromosome 6 which functions in the assembly of the ADA tissue isozymes. In human-mouse hybrids segregating human chromosomes, chromosome 6(+),20(+) hybrids express both ADA-1 and ADA-d; chromosome 6(-),20(+) hybrids express only ADA-1; while 6(+),20(-) hybrids have no human ADA activity. ADA-d formation also occurs in vitro by self-assembly when an extract of human erythrocytes or chromosome 6(-),20(+) hybrids is mixed with a homogenate of chromosome 6(+),20(-) hybrids. The gene on chromosome 6, designated ADCP, codes for an adenosine deaminase complexing protein. The product of ADCP presumably combines with ADA-1 to form the ADA tissue isozymes. The data are consistent with the hypothesis that the distribution of enzymatic activity between ADA-1 and the tissue isozymes depends on the expression of the gene for ADA complexing protein, while the differences in the electrophoretic mobilities of the ADA isozymes, except ADA-1, are generated, as suggested by others, by the degree of glycosylation of the complexing protein.

Gene assignment of alpha-fucosidase and glucose dehydrogenase to the p21 leads to pter region of chromosome 1 in man

Assignment of human genes coding for alpha-fucosidase (alphaFUC) and glucose dehydrogenase (GDH) to chromosome 1 has been confirmed and a location in the p21 leads to pter region demonstrated using man-mouse somatic cell hybrids. The regional location of alphaFUC and GDH was established in cell hybrids using human cells possessing 1/2 translocation chromosomes [46,XX,t(1;2)(p21;q37)]. Hybrids which retained the 2q+ chromosome carrying the 1p21 leads to 1pter region concordantly expressed alphaFUC, GDH, and the short-arm markers ENO1, AK2, and PGM1. Hybrids which retained the 1p21 leads to 1qter region only expressed human PEPC and FH. Data obtained from hybrids in which spontaneous breaks in chromosome 1 had occurred indicate that the gene order in 1p21 leads to 1pter is (ENO1,GDH)-alphaFUC-AK2-PGM1.