The human phosphoglycerate kinase multigene family. HLA-associated sequences and an X-linked locus containing a processed pseudogene and its functional counterpart

The Phosphoglycerate Kinase (PGK) Gene Family of Maize (Zea mays var. B73)

Phosphoglycerate kinase (PGK, E.C. 2.7.2.3) interconverts ADP + 1,3-bisphospho-glycerate (1,3-bPGA) to ATP + 3-phosphoglycerate (3PGA). While most bacteria have a single pgk gene and mammals possess two copies, plant genomes contain three or more PGK genes. In this study, we identified five Pgk genes in the Zea mays var. B73 genome, predicted to encode proteins targeted to different subcellular compartments: ZmPgk1, ZmPgk2, and ZmPgk4 (chloroplast), ZmPgk3 (cytosol), and ZmPgk5 (nucleus). The expression of ZmPgk3 was highest in non-photosynthetic tissues (roots and cobs), where PGK activity was also greatest, consistent with a function in glycolysis. Green tissues (leaf blade and husk leaf) showed intermediate levels of PGK activity, and predominantly expressed ZmPgk1 and ZmPgk2, suggesting involvement in photosynthetic metabolism. ZmPgk5 was weakly expressed and ZmPgk4 was not detected in any tissue. Phylogenetic analysis showed that the photosynthetic and glycolytic isozymes of plants clustered together, but were distinct from PGKs of animals, fungi, protozoa, and bacteria, indicating that photosynthetic and glycolytic isozymes of plants diversified after the divergence of the plant lineage from other groups. These results show the distinct role of each PGK in maize and provide the basis for future studies into the regulation and function of this key enzyme.

Phosphoglycerate kinase 1 (PGK1) in cancer: A promising target for diagnosis and therapy

Phosphoglycerate kinase 1 (PGK1) is the first critical enzyme to produce ATP in the glycolytic pathway. PGK1 is not only a metabolic enzyme but also a protein kinase, which mediates the tumor growth, migration and invasion through phosphorylation some important substrates. Moreover, PGK1 is associated with poor treatment and prognosis of cancers. This manuscript reviews the structure, functions, post-translational modifications (PTMs) of PGK1 and its relationship with tumors, which demonstrates that PGK1 has indispensable value in the tumor progression. The current review highlights the important role of PGK1 in anticancer treatments.

Enzymatic and metabolic characterization of the phosphoglycerate kinase deficiency associated with chronic hemolytic anemia caused by the PGK-Barcelona mutation

Recently, we reported a new mutation of phosphoglycerate kinase (PGK), called PGK-Barcelona, which causes chronic hemolytic anemia associated with progressive neurological impairment. We found a 140T→A substitution that produces an Ile46Asn change located at the N-domain of the enzyme and we suggested that the decrease of the PGK activity is probably related to a loss of enzyme stability. In this paper, by analyzing whole hemolysates and cloned enzymes, we show that both enzymes possess similar kinetic properties (although some differences are observed in the Km values) and the same electrophoretic mobility. However, PGK-Barcelona has higher thermal instability. Therefore, we confirm that the decrease of the red blood cell (RBC) PGK activity caused by the PGK-Barcelona mutation is more closely related to a loss of enzyme stability than to a decrease of enzyme catalytic function. Furthermore, we have measured the levels of glycolytic metabolites and adenine nucleotides in the RBC from controls and from the patient. The increase of 2,3-bisphosphoglycerate and the decrease of ATP RBC levels are the only detected metabolic changes that could cause hemolytic anemia.

PGK deficiency

Phosphoglycerate kinase (PGK) deficiency is one of the relatively uncommon causes of hereditary non-spherocytic haemolytic anaemia (HNSHA). The gene encoding the erythrocyte enzyme PGK1, is X-linked. Mutations of this gene may cause chronic haemolysis with or without mental retardation and they may cause myopathies, often with episodes of myoglobinuria, or a combination of these clinical manifestations. Twenty-six families have been described and in 20 of these the mutations are known. The reason for different clinical manifestations of mutations of the same gene remains unknown.

Molecular characterization of the porcine testis-specificphosphoglycerate kinase 2 (PGK2) gene and its association with male fertility

We have isolated and characterized the porcine testis-specific phosphoglycerate kinase 2 (PGK2) gene, and 1665 bp of full-length PGK2 cDNA were also compiled using modified rapid amplification 5'-RACE and 3'-RACE information. The results of genomic and cDNA sequences of the porcine PGK2 gene demonstrated that it is a single-exon intronless gene with a complete open reading frame of 1251 bp encoding a PGK protein of 417 amino acids. Real-time quantitative PCR results showed that PGK2 mRNA was solely expressed in the testis. There was a lower amount of PGK2 expression in the testis of a 10-month-old herniated boar and a very small amount of PGK2 expression in the testis of an 8-week-old cryptorchid piglet compared to an adult boar. Two SNPs in the PGK2 gene (SNP-A: T427C; SNP-B: C914A) resulting in amino acid substitutions (SNP-A: Ser102-Pro102; SNP-B: Thr264-Lys264) were detected and genotyped among six pig breeds. The nucleotide C at SNP-A responsible for the amino acid exchange to proline could lead to the loss of a casein kinase II (CK2) phosphorylation site in the PGK2 peptide. Association analyses between PGK2 genotypes and several traits of sperm quantity and quality were performed. The results showed that SNP-B has a positive significant effect on semen volume in the breed Pietrain (p = 0.08), i.e., boars carrying genotype CC revealed an increased volume of 49 ml compared with boars having the genotype AA.

A phosphoglycerate kinase mutant (PGK Herlev; D285V) in a Danish patient with isolated chronic hemolytic anemia: mechanism of mutation and structure-function relationships

Phosphoglycerate kinase (PGK) is a X-linked enzyme that plays a key role in the glycolytic pathway. Twelve different variants have already been reported. We describe a new PGK variant, PGK Herlev (Asp 285-->Val), in a 69-year-old Danish patient with isolated chronic hemolysis but who had no neurological or muscular disorders. The description of the mutation is based upon PCR amplification of specific regions of the PGK gene, followed by direct sequencing. Although observed in a male patient, this mutated X-linked gene is expressed partially, i.e., both normal and substituted nucleotides are present at the same position in a ratio of approximately 1:9. The most likely explanation for this observation is based on the occurrence of a somatic mutation of the PGK gene. The relationship of structure to function in PGK Herlev, as well as in all known variants, was examined by the use of a computer model based on the known spatial structure of the yeast and horse enzymes. Such an approach can be generalized to any other protein that has been crystallized and for which x-ray diffraction data are available in a species closely related to man.

The molecular diagnosis of metabolic myopathies

The metabolic myopathies are distinguished by extensive clinical and genetic heterogeneity within and between individual disorders. There are a number of explanations for the variability observed that go beyond single gene mutations or degrees of heteroplasmy in the case of mitochondrial DNA mutations. Some of the contributing factors include protein subunit interactions, tissue-specificity, modifying genetic factors, and environmental triggers. Advances in the molecular analysis of metabolic myopathies during the last decade have not only improved the diagnosis of individual disorders but also helped to characterize the contributing factors that make these disorders so complex.

Multiple elements influence transcriptional regulation from the human testis-specific PGK2 promoter in transgenic mice

The PGK2 gene is expressed in a strictly tissue-specific manner in meiotic spermatocytes and postmeiotic spermatids during spermatogenesis in eutherian mammals. Previous results indicate that this is regulated at the transcriptional level by core promoter sequences that bind ubiquitous transcription factors and by sequences in a 40-base pair (bp) upstream enhancer region (E1/E4) that bind tissue-specific transcription factors. Transgenic mice carrying different PGK2 promoter sequences linked to the chloramphenicol acetyltransferase (CAT) reporter gene, one containing only the 40-bp E1/E4 enhancer sequence plus the core promoter and two containing 515 bp of PGK2 promoter but with either the E1/E4 enhancer region or the Sp1-binding site in the core promoter disrupted by in vitro mutagenesis, all showed levels of expression reduced to less than half that of the wild-type 515 PGK2/CAT transgene. These results indicate that multiple factor-binding regions normally regulate initiation of transcription from the PGK2 promoter. The single disruption of any one of these binding activities reduced, but did not abolish, transgene expression. This is consistent with an "enhanceosome"-like function in this promoter involving multiple bound activator proteins that interact in a combinatorial manner to synergistically promote testis-specific transcription.

Phylogenetic studies of marsupials based on phosphoglycerate kinase DNA sequences

Phosphoglycerate kinase sequences were obtained for 313 aligned bases of 41 individuals from 39 marsupial species. In contrast to previous molecular analyses, the relationships suggested by these data show a high level of congruence with morphologically defined orders and families. Four main monophyletic lineages are recognizable. These are the monogeneric orders Microbiotheria (Dromiciops australis) and Notoryctemorphia (Notoryctes typhlops), a grouping of the American orders Didelphimorphia and Paucituberculata, and the Australasian species other than N. typhlops. Within the Australasian lineage, there are again four main monophyletic groups; the Dasyuridae, two peramelemorph (bandicoot) lineages (one comprised of pseudogene sequences) and the Diprotodontia. This topology is not greatly affected by the exclusion of pseudogenes except that a clade of syndactylous species (Peramelemorphia plus Diprotodontia) is recovered. Two other peramelemorph pseudogenes have inserts of about 1 kb with high levels of similarity to LINE 1 elements. The Diprotodontia is notable for its relative lack of intersequence variation in comparison to the Dasyuromorphia.

A phosphoglycerate kinase mutant (PGK Herlev; D285V) in a Danish patient with isolated chronic hemolytic anemia: mechanism of mutation and structure-function relationships

Phosphoglycerate kinase (PGK) is a X-linked enzyme that plays a key role in the glycolytic pathway. Twelve different variants have already been reported. We describe a new PGK variant, PGK Herlev (Asp 285-->Val), in a 69-year-old Danish patient with isolated chronic hemolysis but who had no neurological or muscular disorders. The description of the mutation is based upon PCR amplification of specific regions of the PGK gene, followed by direct sequencing. Although observed in a male patient, this mutated X-linked gene is expressed partially, i.e., both normal and substituted nucleotides are present at the same position in a ratio of approximately 1:9. The most likely explanation for this observation is based on the occurrence of a somatic mutation of the PGK gene. The relationship of structure to function in PGK Herlev, as well as in all known variants, was examined by the use of a computer model based on the known spatial structure of the yeast and horse enzymes. Such an approach can be generalized to any other protein that has been crystallized and for which x-ray diffraction data are available in a species closely related to man.

Phosphoglycerate kinase pseudogenes in the tammar wallaby and other macropodid marsupials

Phosphoglycerate kinase (EC 2.7.2.3; PGK) exists in two forms in marsupials. PGK1 is an X-linked house-keeping enzyme, and PGK2 is a mainly testis-specific enzyme under autosomal control. We have used PGK1 probes derived from two closely related species of macropodid marsupials (kangaroos and wallabies) to demonstrate the existence of a large family of pseudogenes in the tammar wallaby (Macropus eugenii). Over 30 fragments are detectable after Taq digestion. We estimate that there are 25-30 copies per genome. Most are autosomally inherited and are apparently not closely linked. Only two restriction fragments that appeared to be sex linked could be detected. Varying degrees of hybridization of fragments to the probes suggest different levels of homology, and hence different ages of origin. The existence of two PGK1 homologous restriction fragments from the X and a large number from the autosomes was also demonstrated by somatic cell hybridization for two other macropodid species, the wallaroo (M. robustus) and the red kangaroo (M. rufus). These results are compared with those from human and mouse, and it is suggested that the propensity of PGK1 to form pseudogenes is an ancient (approximately 130 MYR BP) characteristic of mammals. The high level of polymorphism detected in the tammar makes these PGK1 probes potentially useful for measuring genetic variability in this species and other macropodids.

Telomere-associated chromosome fragmentation: applications in genome manipulation and analysis

Telomere-associated chromosome fragmentation (TACF) is a new approach for chromosome mapping based on the non-targeted introduction of cloned telomeres into mammalian cells. TACF has been used to generate a panel of somatic cell hybrids with nested terminal deletions of the long arm of the human X chromosome, extending from Xq26 to the centromere. This panel has been characterized using a series of X chromosome loci. Recovery of the end clones by plasmid rescue produces a telomeric marker for each cell line and partial sequencing will allow the generation of sequence tagged sites (STSs). TACF provides a powerful and widely applicable method for genome analysis, a general way of manipulating mammalian chromosomes and a first step towards constructing artificial mammalian chromosomes.

Structure and expression of the phosphoglycerate kinase (Pgk) gene of Drosophila melanogaster

The gene that encodes phosphoglycerate kinase in Drosophila melanogaster (Pgk) has been isolated and characterized. There is a single copy of Pgk in the Drosophila genome located at cytogenetic position 23A1-2. Transcripts of Pgk are 1.6 kb long and are found during development with a profile similar to the expression pattern of other genes of the glycolytic pathway. There are substantial amounts of maternal transcript in early embryos which decline in abundance until mid-embryogenesis when transcript levels increase; levels remain high, during larval stages, fall during pupariation and rise again at emergence. The nucleotide sequence of the Pgk gene reveals two small introns, one of which is at a position identical to the site of an intron found in Pgk genes from other organisms. The Pgk gene has no TATA box in the region of transcription initiation and has multiple transcription initiation sites that are closely spaced within 110 nucleotides of the translation start site.

PCR derived cDNA clones for X-linked phosphoglycerate kinase-1 in a marsupial, the tammar wallaby (Macropus eugenii)

cDNA clones for the X-linked PGK-1 were obtained from a tammar wallaby liver by PCR and sequenced. The PGK-1 gene published here is the consensus sequence of those clones. The sequence represents an open reading frame of 1251 bp. Sequence comparisons to X-linked and autosomal sequences showed the greatest homology with the X-linked PGK-1 genes in eutherian species. This sequence opens the way for studying the paternal X inactivation phenomenon in marsupials and will assist in defining the time course of mammalian evolution.

Restriction fragment length variants in the marsupialSminthopsis crassicaudata

A fully pedigreed colony of the dasyurid marsupial Sminthopsis crassicaudata has provided material for establishing two panels of DNA samples: a broadbased test panel and a two-generation family panel. These have been used to search for genetic markers in the form of restriction fragment length variants. The molecular probes--pSG-2H, a region of the S. crassicaudata embryonic beta-globin gene; pB8.BS, a region of the human ubiquitin gene, and p3-21a1:1, a region of the processed pseudogene of phosphoglycerate kinase-1 of the macropodid marsupial Macropus robustus--were hybridized to Southern blots of EcoR1-digested DNA from the panels. Analysis of these blots when probed with pSG-2H provided evidence of two alleles segregating at a single EcoR1 site. Analysis of the same blots when probed with pB8.BS suggested allelic variation at two closely linked EcoR1 sites. Probing the blots with p3-21a1:1 produced a complex pattern of bands resembling DNA fingerprints. The presence of a 12.3-kb band was found to conform to a simple autosomal dominant mode of inheritance. Analysis of the family data, for each probe, revealed no significant departure from Mendelian inheritance. This work has provided additional genetic markers that will enhance the use of S. crassicaudata as a model marsupial species and has demonstrated that a high level of genetic variability has been maintained in the marsupial colony.

Isolation and characterization of radiation-reduced hybrids containing portions of the proximal long arm of the human X chromosome: identification of hybrids containing the Menkes' disease locus

The proximal long arm of the human X chromosome (Xcen----Xq13) encompasses an estimated 23 megabases of DNA and contains numerous identified genetic loci. In order to generate a highly enriched source of DNA from this region, radiation-reduced human-hamster hybrids were constructed and screened to identify those that contained at least part of proximal Xq. Eight such hybrids were identified and characterized by Southern blot and fluorescence in situ hybridization analyses to determine more precisely the human DNA complement in each. One hybrid contains the entire proximal long arm and will be useful for mapping Xcen----Xq13 in its entirety and for localizing genes within this region. Another hybrid contains a smaller portion of the proximal long arm that includes the region reported to contain the gene for Menkes' disease.

Physical mapping of 60 DNA markers in the p21.1----q21.3 region of the human X chromosome

Using a panel of human/rodent somatic cell hybrids and human lymphoblast lines segregating 18 different human X-chromosome rearrangements and deletions, we have assigned 60 DNA markers to the physical map of the X chromosome from Xp21.1 to Xq21.3. Data from Southern blot hybridization and polymerase chain reaction (PCR) amplification assign these markers to 15 primary map intervals. This provides a basis for further long-range cloning and mapping of the pericentromeric region of the X chromosome.

Polymorphisms in the coding and noncoding regions of murine Pgk-1 alleles

The mouse X-linked Pgk-1 gene encodes phosphoglycerate kinase. When transfected into human cells, the Pgk-1b allele causes the appearance of mouse PGK-1b enzyme activity. We describe here cloning of mouse Pgk-1a, an allele of Pgk-1 which encodes an enzyme, PGK-1a, with distinct electrophoretic mobility. We constructed recombinants between the DNA encoding Pgk-1b and Pgk-1a and transfected these constructs into human cells to assess the electrophoretic characteristics of each recombinant. In this way the charge variation between the two proteins was localized to exons 4 or 5. Sequencing of these exons revealed a single base-pair difference between the two alleles at codon 155, which predicts the amino acids lysine and threonine in PGK-1b and PGK-1a, respectively. A number of other DNA sequence polymorphisms exist between Pgk-1b and Pgk-1a including part of an L1 repeated element unique to Pgk-1a.

Deletions in processed pseudogenes accumulate faster in rodents than in humans

The relative rates of point nucleotide substitution and accumulation of gap events (deletions and insertions) were calculated for 22 human and 30 rodent processed pseudogenes. Deletion events not only outnumbered insertions (the ratio being 7:1 and 3:1 for human and rodent pseudogenes, respectively), but also the total length of deletions was greater than that of insertions. Compared with their functional homologs, human processed pseudogenes were found to be shorter by about 1.2%, and rodent pseudogenes by about 2.3%. DNA loss from processed pseudogenes through deletion is estimated to be at least seven times faster in rodents than in humans. In comparison with the rate of point substitutions, the abridgment of pseudogenes during evolutionary times is a slow process that probably does not retard the rate of growth of the genome due to the proliferation of processed pseudogenes.

Molecular cloning and sequencing of a murine pgk-1 pseudogene family

Seven genomic mouse DNA fragments carrying pgk-1-homologous regions have been cloned and sequenced. They have to be classified as processed genes because intervening sequences, present in their productive counterpart, are absent. Four pseudogenes (I-IV) represent nearly the complete sequence of pgk-1 cDNA. Two of these genes (I and II), although rather different from the published mouse pgk-1 cDNA in the 3'-untranslated region, represent the actual mouse pgk-1 cDNA sequence in the coding part except for substitutions in the third position of three codons. These genes can code for a functional PGK protein but, lacking as they do classical promoter structures, are probably not expressed. They show the typical characteristics of retroposons, being flanked by A-rich regions and direct repeats which are localized at the positions where the homology with the mouse pgk-1 cDNA is interrupted. Pseudogenes III and IV have numerous mutations. Gene III is also flanked by direct repeats, whereas gene IV is flanked by inverted repeats. The other three genes are flanked by direct repeats localized further inside the target sites. They are truncated and mutated extensively as usually observed with pseudogenes.

Structure of vertebrate genes: a statistical analysis implicating selection

This paper conducts a statistical analysis of the size distribution of exons and six other gene parts [the transcription unit, introns, intervening DNA (sum of introns), mRNA (sum of exons), and leader and trailer regions of mRNA] as well as the number of exons, the percentage of introns, the placement of introns within the gene, and the potential for frameshifts from coding exon shifts. The first seven variables measured in base pairs fit log-normal distributions. Significant correlations between the sizes of intervening DNA and mRNA, the sizes of leader and trailer regions, and the sizes of introns and flanking exons exist. Introns occur at nonrandom frequencies within the codon frame, in untranslated regions, and relative to the frameshift potential from exon movement or duplication. These nonrandom patterns in gene structure demonstrate that models of gene evolution must incorporate selective processes.

The family of mouse phosphoglycerate kinase genes and pseudogenes

The mammalian genome contains two genes encoding phosphoglycerate kinase; the pgk-1 gene is X-linked and is expressed in all cells except sperm, while the pgk-2 gene is expressed exclusively in sperm cells. The mouse genome contains no pseudogenes derived from pgk-2. On the other hand, the genomes of Balb/c and C3H/He strain mice contain six other regions with sequences homologous to those of pgk-1 cDNA. These pgk-related sequences are likely derived from the pgk-1 gene by retroposition because all are located on autosomal chromosomes and because none appear to be interrupted by introns. Two of the presumed pseudogenes contain sequences homologous to all regions of the pgk-1 cDNA while the other four genomic regions were truncated at the 5', 3', or both ends. One of the truncated pseudogenes was sequenced. Its pgk-related sequence was not flanked by direct repeats, suggesting that loss of the 5' and/or 3' ends of this retrogene may have occurred following its integration into the genome. Our evidence suggests that pgk-1-derived retroposons arose initially more than 100 million years ago and have continued to arise until so recently that some are unique to different mouse strains.

Molecular studies of marsupial X chromosomes reveal limited sequence homology of mammalian X-linked genes

To explore the extent to which the X chromosome has been conserved during mammalian evolution, we compared six loci that are X-linked in the human genome with the corresponding genes of the North American marsupial, the Virginia opossum (Didelphis virginiana). Our analysis shows that in the opossum genome there are sequences highly homologous to those of human cDNAs for housekeeping genes, glucose-6-phosphoribosyltransferase (HPRT), phosphoglycerate kinase A (PGK1), and alpha-galactosidase A (GLA). However, ornithine transcarbamylase and blood clotting Factor IX--tissue-specific genes that are X-linked in eutherians mammals--have no highly conserved homologs in the marsupial genome. By cloning opossum G6PD and HPRT, we found that these genes are X-linked in the opossum and that homologous sequences are limited to coding regions. As all genomic fragments hybridizing with the human GLA probe show dosage effects, it is likely that the opossum counterpart is X-linked. Finally, the pattern of hybridization suggests that the autosomal pseudogenes of HPRT and PGK1 in the opossum have remained highly homologous to the human X-linked genes.

Human testis-specific PGK gene lacks introns and possesses characteristics of a processed gene

Phosphoglycerate kinase (PGK) (ATP:3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3) is a metabolic enzyme functioning in the Embden-Meyerhof pathway that converts glucose (or fructose) to pyruvate. Two functional loci for the production of PGK have been identified in the mammalian genome. PGK-1 is an X-linked gene expressed constitutively in all somatic cells and premeitotic germ cells. The human PGK-1 gene consists of 11 exons and 10 introns encompassing a region approximately 23 kilobases (kb) in length. PGK-2 is an autosomal gene expressed in a tissue-specific manner exclusively in the late stages of spermatogenesis. In the present study, a molecular analysis of a human genomic clone of PGK-2 originally isolated by Szabo et al. has revealed that this autosomal sequence completely lacks introns and contains characteristics of a processed gene, or 'retroposon', including the remnants of a poly(A)+ tail and bounding direct repeats. Typically such processed sequences form non-functional pseudogenes that have evolved multiple genetic lesions which preclude translation of any transcript into a functional polypeptide. For example, an X-linked processed pseudogene of PGK-1 (psi PGK-1) in humans has been identified and shown to contain premature termination codons in all reading frames. It was therefore unexpected to find that the intronless autosomal PGK sequence reported here is not a pseudogene, but is rather a functional gene that has retained a complete open reading frame, and is actively expressed in mammalian spermatogenesis. Both the unusual conservation of function in this processed PGK-2 gene and its tissue-specific expression in spermatogenesis are best explained as a compensatory response to the inactivation of the X-linked PGK-1 gene in spermatogenic cells before meiosis.

Nucleotide sequence of the promoter region of a tissue-specific human retroposon: comparison with its housekeeping progenitor

The intronless autosomal phosphoglycerate kinase gene (Pgk-2) is a functional retroposon expressed in a tissue-specific manner in the meiotic and postmeiotic stages of mammalian spermatogenesis. The nucleotide sequence of the promoter region of this gene and its transcription start point are compared with those of Pgk-1, an intron-containing, X-linked, housekeeping gene expressed constitutively in all somatic cells and premeiotic germ cells. The location of flanking direct repeats and apparent conservation of specific regulatory sequences suggest the Pgk-2 retroposon arose from reverse transcriptase-mediated processing of an aberrant Pgk-1 transcript that included the endogenous Pgk-1 promoter elements. Specific sequences that may be involved in mediating differences observed in both the level and cell-type specificity of expression of these genes in spermatogenesis are identified.

Mapping of human autosomal phosphoglycerate kinase sequence to chromosome 19

In order to map human PGK sequences, DNA was prepared from 55 human-mouse somatic cell lines. The DNA was digested to completion with HindIII and Southern filters prepared. These filters were hybridized at high stringency conditions to a human PGK cDNA. Mouse and human X-linked and autosomal bands were distinguished and, in addition to known X-linked sequences, two autosomal PGK sequences were mapped: a 1-kb band to chromosome 19 and a 5-kb band to chromosome 6. The PGK cDNA probe was also hybridized to flow-sorted chromosomes confirming the presence of PGK sequences on the X chromosome and chromosomes 6 and 19.

Phosphoglycerate kinase: studies on normal and a mutant human enzyme

Phosphoglycerate kinase was purified from a number of tissues obtained at autopsy from a subject with the deficiency. Properties of the mutant enzyme were compared to those of PGK purified from tissue obtained from normal subjects. The purified enzyme from the propositus contained two components, a minor fraction (about 2-5%) which behaved similarly to the normal enzyme during the purification procedure, and a major fraction (greater than 95%) which could not be purified by the same procedure. The major fraction demonstrated a number of other properties which differed from the normal. These included a tendency to form aggregates, increased heat sensitivity and altered nucleotide substrate specificity. The smaller fraction appeared to have effectively identical properties to that of the normal enzyme. In keeping with its X-linked mode of inheritance, phosphoglycerate kinase from all normal tissues appeared to have identical kinetic properties, although evidence for minor variations, presumably due to post-translational modifications, was obtained.

Chromatin structure of active and inactive human X-linked phosphoglycerate kinase gene

We have carried out a comparative analysis of DNase I sensitivity of the active and inactive X-linked phosphoglycerate kinase (Pgk) genes in human lymphoblast and fibroblast cultured cells. Three DNase I-sensitive regions were detected: a 5' hypersensitive site, a sensitive region in the interior of the gene and a 3' slightly sensitive site which we previously reported and have now mapped with some precision. A comparison of these sensitive sites in single and multiple X cell lines indicates that the sensitive sites are unique to the active X chromosome. A similar study of an X-linked Pgk pseudogene shows no difference in DNase I sensitivity between the pseudogenes on the active and inactive X chromosomes. These latter results imply that sex chromatin does not confer a unique level of DNase I resistance to DNA on the inactive X chromosome. The exact role of sex chromatin in differential DNase I sensitivity of genes on the inactive and active X chromosomes is discussed.