Isolation and nucleotide sequence of a full-length cDNA coding for aldolase B from human liver

Translation modulation of acid beta-glucosidase in HepG2 cells: participation of the PKC pathway

Acid beta-glucosidase (GCase) is the enzyme deficient in Gaucher disease, a prototypical inherited metabolic error for enzyme and gene therapy. An 80 kDa mammalian cytoplasmic translational control protein (TCP80) modulates GCase translation in vitro and ex vivo by interacting with the 5' coding region of GCase RNA. Ten predicted PKC phosphorylation sites (Ser- or Thr-) are in the TCP80 protein. Phosphorylation of TCP80 in vitro by PKC greatly enhanced its translational inhibitory function using in vitro translation assays; binding of GCase mRNA to TCP80 was unaltered. Conversely, de-phosphorylation of TCP80 reduced its translational inhibitory function. Phosphorylation-related modulation of GCase mRNA translation also was studied in HepG2 cells. GCase expression (protein and activity levels) in HepG2 cells increased (>2-fold) in cells treated with bisindolylmaleimide (BIM), a highly selective PKC specific inhibitor. This correlated with a 90% reduction in TCP80 phosphorylation in the presence of BIM. The amount of TCP80 protein in cytoplasm and its RNA-binding activity were unchanged. These experiments indicate that GCase mRNA translation is modulated by PKC signaling pathways that are mediated through TCP80. These findings indicate potential broader impacts of the TCP/PKC system on expression of this and other genes of therapeutic interest.

Structural and functional analysis of aldolase B mutants related to hereditary fructose intolerance

Hereditary fructose intolerance (HFI) is a recessively inherited disorder of carbohydrate metabolism caused by impaired function of human liver aldolase (B isoform). 25 enzyme-impairing mutations have been identified in the aldolase B gene. We have studied the HFI-related mutant recombinant proteins W147R, A149P, A174D, L256P, N334K and delta6ex6 in relation to aldolase B function and structure using kinetic assays and molecular graphics analysis. We found that these mutations affect aldolase B function by decreasing substrate affinity, maximal velocity and/or enzyme stability. Finally, the functional and structural analyses of the non-natural mutant Q354E provide insight into the catalytic role of Arg(303), whose natural mutants are associated to HFI.

Underexpression of mRNA in human hepatocellular carcinoma focusing on eight loci

Genetic alterations associated with human hepatocellular carcinoma (HCC) have been reported previously, but are not sufficient to specify differences of HCCs from precancerous diseases of the liver, such as hepatitis, hepatic fibrosis, and cirrhosis. In the present study, we performed differential gene display analysis (DGDA) to clarify the specific genetic alterations associated with gene expression changes in the course of development of HCC from chronic viral hepatitis. Four pairs of surgically resected HCCs and hepatitis tissues were investigated. We found 1,028 expression sequence tags (ESTs) that were decreased or increased in HCC tissues compared with hepatitis tissues in the same patient. Nucleotide sequencing showed that they included 55 EST clones in the GenBank database, which were considered candidates for specific messenger RNA (mRNA) expression alterations in HCCs. After excluding 9 ESTs that code mitochondrial DNA, we performed quantitative real-time reverse-transcription polymerase chain reaction (RT-PCR) for the 46 remaining EST clones. We found 8 mRNAs underexpressed in primary HCC tissues in 20 patients in higher percentages than found in previous studies, including 18 cases (90%) for aldolase B (ALDOB), 15 cases (75%) for carbamyl phosphate synthetase 1 (CPS1), albumin (ALB), plasminogen (PLG), and EST 51549, 13 cases (65%) for cytochrome P450 subfamily 2E1 (CYP2E1), 12 cases (60%) for human retinol-binding protein 4 (RBP4), and 11 cases (55%) for human organic anion transporter C (OATP-C) gene. In conclusion, underexpression of key gene products may be important in the development and/or progression of HCC.

PCR and in situ hybridization studies of telomerase subunits in human non-neoplastic livers

Telomerase, a ribonucleoprotein enzyme associated with cellular immortality, consists of human telomerase RNA component (hTERC), human telomerase protein 1 (hTEP1), and human telomerase reverse transcriptase (hTERT). In this study, the expression of these subunits was examined in non-neoplastic livers [13 cases of chronic viral hepatitis (CVH), 16 of primary biliary cirrhosis (PBC), two of primary sclerosing cholangitis, and six normal livers], using the reverse transcription-polymerase chain reaction (RT-PCR), nested PCR, and in situ hybridization (ISH). Six hepatocellular carcinoma (HCC) cases and one colonic cancer were used as positive controls. Telomeric repeat amplification protocol (TRAP) assay disclosed distinct telomerase activity in all positive controls and weak telomerase activity in non-neoplastic livers in 4 of 13 CVH cases and 5 of 16 PBC cases. By RT- and nested PCR, both hTERC and hTEP1 mRNA were detectable in all non-neoplastic liver tissues; ISH revealed hTERC and hTEP1 mRNA in the periportal and periseptal hepatocytes and inflammatory mononuclear cells in those cases examined. ISH revealed hTERT mRNA only in a few infiltrating mononuclear cells in 3 of 13 CVH and 2 of 16 PBC livers and these five cases were also positive by TRAP assay. In four of these five cases, hTERT mRNA was also detectable by nested PCR, suggesting that hTERT mRNA in the non-neoplastic liver is expressed by infiltrating mononuclear cells. Biliary epithelial cells were totally negative for these human telomerase subunits. Three subunits were constantly detected in all positive controls by ISH as well as by RT- and nested PCR. The finding that hTERC and hTEP1 mRNA, but not hTERT mRNA, were detectable in the non-neoplastic hepatocytes suggests that telomerase is present but not activated and that additional factor(s) are necessary for the expression of hTERT mRNA in the hepatocytes, along with immortalization and neoplastic transformation.

Functional and molecular modelling studies of two hereditary fructose intolerance-causing mutations at arginine 303 in human liver aldolase

We have identified a novel hereditary fructose intolerance mutation in the aldolase B gene (i.e. liver aldolase) that causes an arginine-to-glutamine substitution at residue 303 (Arg(303)-->Gln). We previously described another mutation (Arg(303)-->Trp) at the same residue. We have expressed the wild-type protein and the two mutated proteins and characterized their kinetic properties. The catalytic efficiency of protein Gln(303) is approx. 1/100 that of the wild-type for substrates fructose 1,6-bisphosphate and fructose 1-phosphate. The Trp(303) enzyme has a catalytic efficiency approx. 1/4800 that of the wild-type for fructose 1,6-bisphosphate; no activity was detected with fructose 1-phosphate. The mutation Arg(303)-->Trp thus substitution impairs enzyme activity more than Arg(303)-->Gln. Three-dimensional models of wild-type, Trp(303) and Gln(303) aldolase B generated by homology-modelling techniques suggest that, because of its larger size, tryptophan exerts a greater deranging effect than glutamine on the enzyme's three-dimensional structure. Our results show that the Arg(303)-->Gln substitution is a novel mutation causing hereditary fructose intolerance and provide a functional demonstration that Arg(303), a conserved residue in all vertebrate aldolases, has a dominant role in substrate binding during enzyme catalysis.

Isolation and characterization of Xenopus laevis aldolase B cDNA and expression patterns of aldolase A, B and C genes in adult tissues, oocytes and embryos of Xenopus laevis

Following previous cloning and expression studies of Xenopus aldolase C (brain-type) and A (muscle-type) cDNAs, we cloned here two Xenopus aldolase B (liver-type) cDNAs (XALDB1 and XALDB2, 2447 and 1490 bp, respectively) using two different liver libraries. These cDNAs had very similar ORF with only one conservative amino acid substitution, but 3'-UTR of XALDB1 contained ca. 1 kb of unrelated reiterated sequence probably ligated during library construction as shown by genomic Southern blot analysis. In adult, aldolase B mRNA (ca. 1.8 kb) was expressed strongly in kidney, liver, stomach, intestine, moderately strongly in skin, and very weakly in all the other tissues including muscles and brain, which strongly express aldolase A and C mRNAs, respectively. In oocytes and early embryos, aldolase A and C mRNAs occurred abundantly as maternal mRNAs, but aldolase B mRNA occurred only at a residual level, and its strong expression started only after the late neurula stage, mainly in liver rudiment, pronephros, epidermis and proctodeum. Thus, active expression of the gene for aldolase B, involved in dietary fructose metabolism, starts only later during development (but before the feeding stage), albeit genes for aldolases A and C, involved in glycolysis, are expressed abundantly from early stages of embryogenesis, during which embryos develop depending on yolk as the only energy source.

Cloning of a brain-type aldolase cDNA and changes in its mRNA level during oogenesis and early embryogenesis in Xenopus laevis

A full length cDNA clone (cXALD3) for Xenopus laevis aldolase mRNA, which exists abundantly in oocytes, was isolated from Xenopus laevis ovary cDNA library, and its nucleotide sequence was determined. The cDNA was 1.8 kb in length and encoded 363 amino acids. From the deduced amino acid sequence and the Northern blot analysis of the RNAs from several adult tissues, this clone was concluded to be a brain-type aldolase gene. The XALD3 mRNA level per egg or embryo was high during early oogenesis, but was markedly reduced during late oogenesis and was maintained at low level during early embryogenesis until it started to increase at the late neurula stage. The mRNA was also detected in testis. The characteristic change in the temporal pattern of expression and the distribution of XALD3 mRNA among different tissues suggest a possibility that brain type aldolase may play some important roles in gametogenesis and in neurulation.

The molecular basis of hereditary fructose intolerance in Italian children

We investigated the molecular defects of the aldolase B gene in five unrelated patients affected by hereditary fructose intolerance. The techniques used were DNA amplification, direct sequencing and allele-specific oligonucleotide (ASO) hybridization. The most frequent substitutions found in the hereditary fructose intolerance alleles analysed were the A174D and the A149P mutations, which account for 50% and 30% of the alleles, respectively. In two unrelated families, we found a rare mutation, the MD delta 4 previously described only in one British family, which may be an important cause of the disease in Italy.

Cis-acting elements in the promoter region of the human aldolase C gene

We investigated the cis-acting sequences involved in the expression of the human aldolase C gene by transient transfections into human neuroblastoma cells (SKNBE). We demonstrate that 420 bp of the 5'-flanking DNA direct at high efficiency the transcription of the CAT reporter gene. A deletion between -420 bp and -164 bp causes a 60% decrease of CAT activity. Gel shift and DNase I footprinting analyses revealed four protected elements: A, B, C and D. Competition analyses indicate that Sp1 or factors sharing a similar sequence specificity bind to elements A and B, but not to elements C and D. Sequence analysis shows a half palindromic ERE motif (GGTCA), in elements B and D. Region D binds a transactivating factor which appears also essential to stabilize the initiation complex.

Identification of transglutaminase substrates in HT29 colon cancer cells: use of 5-(biotinamido)pentylamine as a transglutaminase-specific probe

A biotinamine probe, 5-(biotinamido)pentylamine, was used for biotin-labeling of proteins in HT29 colon cancer cell extracts by endogenous transglutaminase activity. The biotin-labeled protein substrates were isolated and recovered by avidin-affinity chromatography. The proteins were separated using SDS-polyacrylamide gel electrophoresis, electroblotted onto a polyvinylidene difluoride membrane, visualized using Coomassie blue, cut out, and sequenced. Amino acid sequence data identified human fructose-1,6-bisphosphate aldolase A, an intracellular protein, as a substrate for cellular transglutaminase.

Case report: heterogeneity of aldolase B in hereditary fructose intolerance

Hereditary fructose intolerance (HFI) is a recessive genetic disorder with an estimated disease frequency of 1 in 20,000 and a carrier frequency of 1 in 70. Affected individuals are unable to assimilate fructose from fruit sugars and may develop severe hypoglycemia, metabolic problems, and death if misdiagnosed. Those who survive childhood learn to avoid sweets, effectively preventing further symptoms and complications. The disease is caused by a genetically defective hepatic enzyme, aldolase B. Traditionally, diagnosis has been made by intravenous fructose challenge or by liver biopsy, both difficult and risky invasive tests. Identification of mutations of the aldolase B gene by analysis of DNA from blood leukocytes is now possible, allowing for potential noninvasive diagnosis of subjects at risk in the future. The authors demonstrate heterozygosity for an aldolase B gene mutation in a patient with HFI.

Expression of the rat aldolase B gene: a liver-specific proximal promoter and an intronic activator

The nature and location of the cis-acting DNA sequences regulating expression of the rat aldolase B gene has been investigated. Two liver-specific DNAse I hypersensitive sites were detected, one located just upstream from the cap site, the second in the middle of the first, 4.8-kbp-long, intron. A fragment of 190 bp 5' to the cap site behaved as a tissue-specific but weak core promoter: it directed a detectable reporter gene expression in the Hep G2 cells and hepatocytes, but not in fibroblasts. The tissue-specific expression was stimulated at least 16 fold when constructs contained the entire first intron. The intronic activating sequences could be ascribed to an inner 2 kbp fragment in which the downstream liver-specific DNAse I hypersensitive site was located.

Aldolase B mutations in Italian families affected by hereditary fructose intolerance

Hereditary fructose intolerance (HFI) is an inborn error of metabolism caused by aldolase B deficiency. The aldolase B gene has been cloned and the following mutations causing HFI have been identified: A149P (a G----C transversion in exon 5), A174D (a C----A transversion in exon 5), L288 delta C (a base pair deletion in exon 8), and N334K (a G----C transversion in exon 9). We have investigated the occurrence of these mutations in 11 Italian patients affected by HFI using PCR and hybridisation to specific oligomers. We found that four patients were homozygous for the A149P mutation, two patients were homozygous for the A174D mutation, three patients were compound heterozygotes for both the A149P and A174D mutations, one patient was homozygous for the N334K mutation, and one patient did not show any of the reported mutations (HFI diagnosis carried out by aldolase B assay). The L288 delta C mutation has not been found in this survey.

Characterization of the transcription-initiation site and of the promoter region within the 5' flanking region of the human aldolase C gene

Several aldolase C clones from a human genomic library have been identified using a mouse aldolase C cDNA as a hybridization probe. The most complete fragment of the clones identified is 14 kb long and contains the complete aldolase C gene. The nucleotide sequence analysis of more than 5 kb includes the intron/exon organization structure of the gene and the 3' and 5' flanking regions. Although no human cDNA is yet available, a canonical polyadenylation signal at the 3' end of the gene indicates the proximity of the poly(A) addition site. We have analyzed the 5' noncoding region by S1 mapping and primer-extension experiments. The transcription-initiation sites for the human aldolase C gene in brain tissue was located about 1300 bp upstream from the methionine initiation codon. Preliminary functional assays of the promoter by transfection into rat glioma cells have indicated that promoter elements lie between positions -161 and -416 from the start point of transcription.

Assignment of human aldolase C gene to chromosome 17, region cen----q21.1

The mapping of the gene coding for human aldolase C has been studied using a specific cDNA probe and genomic blots from a panel of human-hamster somatic cell hybrids. The results show that the aldolase C gene is on chromosome 17. In situ experiments have restricted the mapping to the region 17cen----q21.1. Using the same panel of human-hamster somatic cell hybrids, we have confirmed the localization of aldolase A and B on chromosomes 16 and 9, respectively.

The brain-specific gene for rat aldolase C possesses an unusual housekeeping-type promoter

A DNA fragment encompassing the first exon and about 750 bp of the 5'-flanking sequence has been isolated and sequenced. The gene has multiple start sites of transcription which are dispersed over about 200 bp. The promoter lacks TATA and CAAT boxes and is very G + C-rich, with putative binding sites for the transcriptional factors Sp1 and AP2. Similar features are shared with two other brain-specific genes encoding thy-1 antigen and gamma-enolase. The existence of a conserved block of similarity upstream of the human and rat aldolase C genes suggests that this region could be involved in tissue-specific expression whose mechanism seem to be, at least in part, transcriptional.

Construction and expression of human aldolase A and B expression plasmids in Escherichia coli host

E. coli expression plasmids for human aldolases A and B (EC 4.1.2.13) have been constructed from the pIN-III expression vector and their cDNAs, and expressed in E. coli strain JM83. Enzymatically active forms of human aldolase have been generated in the cells when transfected with either pHAA47, a human aldolase A expression plasmid, or pHAB 141, a human aldolase B expression plasmid. These enzymes are indistinguishable from authentic enzymes with respect to molecular size, amino acid sequences at the NH2- and COOH-terminal regions, the Km for substrate, fructose 1,6-bisphosphate and the activity ratio of fructose 1,6-bisphosphate/fructose 1-phosphate (FDP/F1P), although net electric charge and the Km for FDP of synthetic aldolase B differed from those for a previously reported human liver aldolase B. In addition, both the expressed aldolases A and B complement the temperature-sensitive phenotype of the aldolase mutant of E. coli h8. These data argue that the expressed aldolases are structurally and functionally similar to the authentic human aldolases, and would provide a system for analysis of the structure-function relationship of human aldolases A and B.

Cloning, sequence analysis and over-expression of the gene for the class II fructose 1,6-bisphosphate aldolase of Escherichia coli

Nucleotide sequence analysis of the Escherichia coli chromosomal DNA inserted in the plasmid pLC33-5 of the Clarke and Carbon library [Clarke & Carbon (1976) Cell 9, 91-99] revealed the existence of the gene, fda, encoding the Class II (metal-dependent) fructose 1,6-bisphosphate aldolase of E. coli. The primary structure of the polypeptide chain inferred from the DNA sequence of the fda gene comprises 359 amino acids, including the initiating methionine residue, from which an Mr of 39,146 could be calculated. This value is in good agreement with that of 40,000 estimated from sodium dodecyl sulphate-polyacrylamide gel electrophoresis of the purified dimeric enzyme. The amino acid sequence of the Class II aldolase from E. coli showed no homology with the known amino acid sequences of Class I (imine-forming) fructose 1,6-bisphosphate aldolases from a wide variety of sources. On the other hand, there was obvious homology with the N-terminal sequence of 40 residues already established for the Class II fructose 1,6-bisphosphate aldolase of Saccharomyces cerevisiae. These Class II aldolases, one from a prokaryote and one from a eukaryote, evidently are structurally and evolutionarily related. A 1029 bp-fragment of DNA incorporating the fda gene was excised from plasmid pLC33-5 by digestion with restriction endonuclease HaeIII and subcloned into the expression plasmid pKK223-3, where the gene came under the control of the tac promoter. When grown in the presence of the inducer isopropyl-beta-D-thiogalactopyranoside, E. coli JM101 cells transformed with this recombinant expression plasmid generated the Class II fructose 1,6-bisphosphate aldolase as approx. 70% of their soluble protein. This unusually high expression of an E. coli gene should greatly facilitate purification of the enzyme for any future structural or mechanistic studies.

Human aldolase A gene. Structural organization and tissue-specific expression by multiple promoters and alternate mRNA processing

The complete nucleotide sequence of the human aldolase A isoenzyme gene is reported. The cloned gene sequence, spanning 7530 bp, includes twelve exons and occurs as a single copy per haploid human genome. The structural organization of the gene is quite complex: eight exons containing the coding sequence are common to all mRNAs extracted from human and other mammalian sources; four additional exons are present in the 5' untranslated region, of these one is contained in the ubiquitous type of mRNA, the second is in the muscle-specific type of mRNA and the third and fourth are in a minor species of mRNA found in human liver tissue. Furthermore, the determined sequence includes 1000 nucleotides upstream from the first exon (exon I) in the 5' flanking region, and 400 nucleotides, which include the polyadenylation signal, downstream from the termination codon. S1-nuclease-protection analysis of the 5' end of mRNA extracted from human cultured fibroblasts, muscle and hepatoma cell lines indicates the existence of four different transcription-initiation sites. The latter are also supported by the presence of conventional sequences for eukaryotic promoters. Therefore, the four promoters on the same gene generate different tissue-specific transcripts, which share the translated sequence, but each has a unique 5' untranslated region as a result of differential mRNA processing. The nucleotide homology at the coding region and the intron-exon organization of the three human and mammalian aldolase A, B and C genes confirm that they arose from a common ancestral gene, and that aldolase B diverged first.

Catalytic deficiency of human aldolase B in hereditary fructose intolerance caused by a common missense mutation

Hereditary fructose intolerance (HFI) is a human autosomal recessive disease caused by a deficiency of aldolase B that results in an inability to metabolize fructose and related sugars. We report here the first identification of a molecular lesion in the aldolase B gene of an affected individual whose defective protein has previously been characterized. The mutation is a G----C transversion in exon 5 that creates a new recognition site for the restriction enzyme Ahall and results in an amino acid substitution (Ala----Pro) at position 149 of the protein within a region critical for substrate binding. Utilizing this novel restriction site and the polymerase chain reaction, the patient was shown to be homozygous for the mutation. Three other HFI patients from pedigrees unrelated to this individual were found to have the same mutation: two were homozygous and one was heterozygous. We suggest that this genetic lesion is a prevailing cause of hereditary fructose intolerance.

The structure of brain-specific rat aldolase C mRNA and the evolution of aldolase isozyme genes

The cDNA clones for rat aldolase C mRNA having the nearly complete length were isolated from a rat brain cDNA library and sequenced. The nucleotide sequence of pRAC2-1, a cDNA clone having the largest cDNA insert, indicates that the cDNA is composed of a 105-base-pair 5'-noncoding sequence, a 1089-base-pair coding-sequence and a 382-base-pair 3'-noncoding sequence. The amino acid sequence of aldolase C deduced from a possible open reading frame was composed of 362 residues having a relative molecular mass of 39,164 excluding the initiating methionine, one amino acid shorter than aldolases A and B. The length of aldolase c mRNA was 1750 residues, somewhat longer than that of the aldolase A and B transcripts. The aldolase C mRNA was distributed mainly in the brain, some in ascites hepatoma and fetal liver. Comparison of the amino acid sequences of rat aldolase C with those for rat aldolase A and B [Joh et al. (1985) Gene 39, 17-24; Tsutsumi et al. (1984) J. Biol. Chem. 259, 14572-14575], which have been determined previously, shows the existence of highly conserved stretches of amino acid among the three isozymic forms throughout their sequences. The extent of the homology between aldolases A and C is 81%, while those between aldolases A and B, and B and C are 70%, respectively. The analysis of amino acid substitution among aldolases A, B and C from several species suggests that the isozyme genes diverged much earlier than animal species appeared and that the aldolase C gene has evolved from the aldolase A gene after aldolase A and B genes diverged.

Mapping of a restriction fragment length polymorphism within the human aldolase B gene

Peripheral blood DNA was hybridized to the full-length cDNA and the cloned structural gene of human aldolase B. With PvuII endonuclease a restriction fragment length polymorphism was detected that was present in the heterozygous state in about 21% of the individuals tested. A map of the human aldolase gene was constructed for the two groups of individuals found to produce different fragments after PvuII digestion. This allowed the localization of the polymorphic site within the gene, which was found to be due to the loss of a PvuII site in the last intron upstream from the 3' end. This polymorphism may be used as a genetic marker to study individuals affected by hereditary fructose intolerance.

Isolation and sequence analysis of a cDNA clone encoding the entire catalytic subunit of phosphorylase kinase

Synthetic oligonucleotides have been used to isolate a 1.85 kb clone containing the full length coding sequence for the catalytic subunit of rabbit skeletal muscle phosphorylase kinase from a cDNA library constructed in lambda gt10. Sequence analysis of the clone predicted an amino acid sequence in agreement with a published primary structure. Inspection of the codon usage revealed a strong preference for G or C nucleotides at the third codon position as found for several other skeletal muscle proteins. This cDNA clone should facilitate identification of functional domains, including the calmodulin-binding site, and investigation of the molecular basis of X-linked phosphorylase kinase deficiencies.

Molecular gene mapping of human aldolase A (ALDOA) gene to chromosome 16

Mapping of human aldolase A (ALDOA) gene was performed by molecular hybridization techniques using a panel of human-mouse cell hybrids and sorted fractions of human metaphase chromosomes besides in situ hybridization. For the purpose, three kinds of DNA probes derived from the coding region (probe-1), the 3' noncoding region (probe-2), and the coding and 3' noncoding regions (probe-3) of human aldolase A cDNA clone, pHAAL116-3, were selectively employed. The results of RNA and DNA blot analyses indicated that the human ALDOA gene is located on chromosome 16. The in situ hybridization experiment also indicated that the ALDOA gene was localized to 16q22-q24.

A new human species of aldolase A mRNA from fibroblasts

A full-length cDNA aldolase A clone was isolated from a human fibroblast cDNA library and completely sequenced. Excluding the poly(A) tail, the clone covers 1095 base pairs (bp) of the coding region, plus 199 bp downstream for the termination codon and 146 bp upstream for the initiation codon, within a total of 1440 bp. Primer extension experiments performed with human cultured fibroblast mRNA indicate an elongated product of a further 40 bp. These results evaluated together with those obtained in a concurrent study concerning aldolase A mRNA isolated from human liver are direct evidence of aldolase A mRNA multiplicity in man. The data also suggest the existence in mammals of three different classes of aldolase A mRNA, which would account for tissue specificity and resurgence of foetal expression in tumors.

Molecular cloning and expression of rat aldolase C messenger RNA during development and hepatocarcinogenesis

A rat brain cDNA library was screened at low stringency with an aldolase B cDNA probe corresponding to the coding sequence of the mRNA, then at high stringency with a 3' non-coding aldolase A cDNA probe. One clone, which hybridized only under the first conditions, was further characterized and used to screen the library again. Two overlapping clones, complementary to aldolase C mRNA, were obtained. They cover the 113 carboxy-terminal coding residues and the 3' non-coding region up to the poly(A) tail. Their nucleotide sequence was determined. In the coding region the overall homology with aldolase A was 67% at the nucleotide level and 76% at the protein level. With aldolase B these values were 63% and 65% respectively. The 3' non-coding region was 380 bases long and did not exhibit any homology with the untranslated 3' extension of aldolase A and B mRNAs. Southern blot analysis indicates that probably a single aldolase C gene exists per haploid genome. Aldolase C mRNA was detected at low concentration in practically all the foetal tissues and its expression markedly and rapidly decreased after birth. In brain the concentration of aldolase C mRNA remained high and stable even after birth. Aldolase C mRNA is approximately 50-fold more abundant in brain than in foetal tissues, which are the richest in messenger RNA. In the course of azo-dye hepatocarcinogenesis the aldolase C gene is re-expressed early, with a maximum at the 4th week of carcinogenic diet, which probably corresponds to the maximal proliferation of the oval cells.

Sequence analysis of the cDNA encoding human liver glycogen phosphorylase reveals tissue-specific codon usage

We have cloned the cDNA encoding glycogen phosphorylase (1,4-alpha-D-glucan:orthophosphate alpha-D-glucosyl-transferase, EC 2.4.1.1) from human liver. Blot-hybridization analysis using a large fragment of the cDNA to probe mRNA from rabbit brain, muscle, and liver tissues shows preferential hybridization to liver RNA. Determination of the entire nucleotide sequence of the liver message has allowed a comparison with the previously determined rabbit muscle phosphorylase sequence. Despite an amino acid identity of 80%, the two cDNAs exhibit a remarkable divergence in G+C content. In the muscle phosphorylase sequence, 86% of the nucleotides at the third codon position are either deoxyguanosine or deoxycytidine residues, while in the liver homolog the figure is only 60%, resulting in a strikingly different pattern of codon usage throughout most of the sequence. The liver phosphorylase cDNA appears to represent an evolutionary mosaic; the segment encoding the N-terminal 80 amino acids contains greater than 90% G+C at the third codon position. A survey of other published mammalian cDNA sequences reveals that the data for liver and muscle phosphorylases reflects a bias in codon usage patterns in liver and muscle coding sequences in general.

Expression of three mRNA species from a single rat aldolase A gene, differing in their 5' non-coding regions

The complete nucleotide sequence of the rat aldolase A isozyme gene, including the 5' and 3' flanking sequences, was determined. The gene comprises ten exons, spans 4827 base-pairs and occurs in a single copy per haploid rat genome. The genomic DNA sequence was compared with those of three species of rat aldolase A mRNA (mRNAs I, II and III) that have been found to differ from each other only in the 5' non-coding region and to be expressed tissue-specifically. It revealed that the first exon (exon M1) encodes the 5' non-coding sequence of mRNA I, while the second exon (exon AH1) encodes those of mRNAs II and III and the following eight exons (exons 2 to 9) are shared commonly by all the mRNA species. These results allowed us to conclude that mRNA I and mRNAs II, III were generated from a single aldolase A gene by alternative usage of exon M1 or exon AH1 in addition to exons 2 to 9. S1 nuclease mapping of the 5' ends of their precursor RNAs suggested that these three mRNA species were transcribed from three different initiation sites on the single gene.

Human aldolase B cDNA detects a Pvu II RFLP in healthy individuals

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Structure and expression of mouse aldolase genes. Brain-specific aldolase C amino acid sequence is closely related to aldolase A

Brain-specific aldolase C amino acid sequence (greater than 75% of the coding region) was determined for the first time. Two cDNA clones, pAM1 and pAM2, were identified, from a mouse brain library, by using human aldolase B cDNA as a probe. The larger one, pAM2, identified as a cDNA for aldolase C, has been completely sequenced and covers the 5'-untranslated region of the mRNA and the codons for amino acids 1-227 of the protein. The sequence indicates that aldolase C is more akin to aldolase A than to aldolase B. A cDNA library from mouse muscle was also screened, allowing the identification of clones pAM3 and pAM4, which contain cDNAs for aldolase A. The sequence obtained from pAM3 covers 70% of the coding sequence (amino acids 99-355) from the -COOH part of the protein. The cDNAs for the three aldolases, A, B and C, have been hybridized to RNA from various rat tissues. The results confirm the tissue specificity of the expression of the mRNA for the different isoenzymes and support the hypothesis that aldolase C expression, as aldolase A and B, is regulated at the transcriptional level or, in any case, via mRNA concentration.

Nucleotide sequence of a cDNA clone for human aldolase: a messenger RNA in the liver

Nearly complete cDNA clones for human aldolase A mRNA were isolated from human liver cDNA library and the nucleotide sequence determined. Using the cDNA clone as a probe the length of human aldolase A mRNAs, isolated from the skeletal muscle, liver and placenta tissues, was measured by RNA blotting and estimated to be 1,600 nucleotides for skeletal muscle mRNA and 1,700 nucleotides for both the liver and placenta mRNAs, indicating that different species of mRNA coding for human aldolase A were expressed in the different tissues.

Human aldolase isozyme gene: the structure of multispecies aldolase B mRNAs

A complete nucleotide sequence of human aldolase B mRNA was determined with a recombinant cDNA (pHABL120-3). The cDNA insert was composed of 1,652 bases excluding poly(A) tail and the sequence was consistent with the previous results reported by others. However, S1 nuclease mapping and subsequent genomic analysis allowed us to know that the clone possesses two more sites corresponding to 5'-termini in the 5'-noncoding region and another site of polyadenylation in the 3'-noncoding region. In fact, the major aldolase B mRNA species occupying 90% of the total mRNAs initiated at the predominant position corresponding to the position around -82 of the 5'-noncoding sequence in pHABL120-3 and terminated at the distal polyadenylation site. Second species accounting for 9% of the mRNAs initiated at the same site and terminated at the proximal polyadenylation site. The remainings have a longer 5'-noncoding sequence which starts from further upstream region of the major one and pHABL120-3 corresponds to one of these largest clones.

Rat aldolase A messenger RNA: the nucleotide sequence and multiple mRNA species with different 5'-terminal regions

The nucleotide sequence of aldolase A mRNA in rat skeletal muscle was determined using recombinant cDNA clones and a cDNA synthesized by primer extension. The sequence is composed of 1343 nucleotides (nt) except for the poly(A) tail. Based on the sequence analysis we have deduced an open reading frame with 363 amino acids (aa) (Mr 39134). The sequence suggests several nt polymorphisms in the mRNA population, one of which causes an aa change. The determined sequence of rat aldolase A mRNA was compared with the published ones of rabbit aldolase A or rat aldolase B mRNAs. The homology between rat and rabbit aldolase A mRNA sequences is greater than that between rat aldolase A and B mRNA sequences. Multiple aldolase A mRNAs having different Mrs were detected in the various tissues, and appeared to be expressed in a tissue-specific manner. Further analysis suggests that differences in mRNA length are due to differences in the 5'-noncoding terminal region.