Cloning, characterization, expression, and chromosomal localization of a human ferritin heavy-chain gene

Pin1 and Alzheimer's disease

Alzheimer's disease (AD) is an immense and growing public health crisis. Despite over 100 years of investigation, the etiology remains elusive and therapy ineffective. Despite current gaps in knowledge, recent studies have identified dysfunction or loss-of-function of Pin1, a unique cis-trans peptidyl prolyl isomerase, as an important step in AD pathogenesis. Here I review the functionality of Pin1 and its role in neurodegeneration.

Environmental impact on carcinogenesis under BRCA1 haploinsufficiency

Cancer is the primary cause of human mortality in Japan since 1981. Although numerous novel therapies have been developed and applied in clinics, the number of deaths from cancer is still increasing worldwide. It is time to consider the strategy of cancer prevention more seriously. Here we propose a hypothesis that cancer can be side effects of long time-use of iron and oxygen and that carcinogenesis is an evolution-like cellular events to obtain "iron addiction with ferroptosis-resistance" where genes and environment interact each other. Among the recognized genetic risk factors for carcinogenesis, we here focus on BRCA1 tumor suppressor gene and how environmental factors, including daily life exposure and diets, may impact toward carcinogenesis under BRCA1 haploinsufficiency. Although mice models of BRCA1 mutants have not been successful for decades in generating phenotype mimicking the human counterparts, a rat model of BRCA1 mutant was recently established that reasonably mimics the human phenotype. Two distinct categories of oxidative stress, one by radiation and one by iron-catalyzed Fenton reaction, promoted carcinogenesis in Brca1 rat mutants. Furthermore, mitochondrial damage followed by alteration of iron metabolism finally resulted in ferroptosis-resistance of target cells in carcinogenesis. These suggest a possibility that cancer prevention by active pharmacological intervention may be possible for BRCA1 mutants to increase the quality of their life rather than preventive mastectomy and/or oophorectomy.

Behavioral innovation and genomic novelty are associated with the exploitation of a challenging dietary opportunity by an avivorous bat

Foraging on nocturnally migrating birds is one of the most challenging foraging tasks in the animal kingdom. Only three bat species (e.g., Ia io) known to date can prey on migratory birds. However, how these bats have exploited this challenging dietary niche remains unknown. Here, we demonstrate that I. io hunts at the altitude of migrating birds during the bird migration season. The foraging I. io exhibited high flight altitudes (up to 4945 m above sea level) and high flight speeds (up to 143.7 km h⁻¹). I. io in flight can actively prey on birds in the night sky via echolocation cues. Genes associated with DNA damage repair, hypoxia adaptation, biting and mastication, and digestion and metabolism have evolved to adapt to this species’ avivorous habits. Our results suggest that the evolution of behavioral innovation and genomic novelty are associated with the exploitation of challenging dietary opportunities.

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Predation on nocturnally migrating birds is rare and challenging in nature

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Bats exhibit high flight altitude and speed associated with foraging on migrating birds

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Bats can actively prey on birds in the night sky via echolocation cues

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The adaptive evolution of genes enables bats to adapt to the avivorous habits

The Role of Iron Regulation in Immunometabolism and Immune-Related Disease

Immunometabolism explores how the intracellular metabolic pathways in immune cells can regulate their function under different micro-environmental and (patho-)-physiological conditions (Pearce, 2010; Buck et al., 2015; O'Neill and Pearce, 2016). In the last decade great advances have been made in studying and manipulating metabolic programs in immune cells. Immunometabolism has primarily focused on glycolysis, the TCA cycle and oxidative phosphorylation (OXPHOS) as well as free fatty acid synthesis and oxidation. These pathways are important for providing the energy needs of cell growth, membrane rigidity, cytokine production and proliferation. In this review, we will however, highlight the specific role of iron metabolism at the cellular and organismal level, as well as how the bioavailability of this metal orchestrates complex metabolic programs in immune cell homeostasis and inflammation. We will also discuss how dysregulation of iron metabolism contributes to alterations in the immune system and how these novel insights into iron regulation can be targeted to metabolically manipulate immune cell function under pathophysiological conditions, providing new therapeutic opportunities for autoimmunity and cancer.

A FTH1 gene:pseudogene:microRNA network regulates tumorigenesis in prostate cancer

Non-coding RNAs play a vital role in diverse cellular processes. Pseudogenes, which are non-coding homologs of protein-coding genes, were once considered non-functional evolutional relics. However, recent studies have shown that pseudogene transcripts can regulate their parental transcripts by sequestering shared microRNAs (miRNAs), thus acting as competing endogenous RNAs (ceRNAs). In this study, we utilize an unbiased screen to identify the ferritin heavy chain 1 (FTH1) transcript and multiple FTH1 pseudogenes as targets of several oncogenic miRNAs in prostate cancer (PCa). We characterize the critical role of this FTH1 gene:pseudogene:miRNA network in regulating tumorigenesis in PCa, whereby oncogenic miRNAs downregulate the expression of FTH1 and its pseudogenes to drive oncogenesis. We further show that impairing miRNA binding and subsequent ceRNA crosstalk completely rescues the slow growth phenotype in vitro and in vivo. Our results also demonstrate the reciprocal regulation between the pseudogenes and intracellular iron levels, which are crucial for multiple physiological and pathophysiological processes. In summary, we describe an extensive gene:pseudogene network comprising multiple miRNAs and multiple pseudogenes derived from a single parental gene. The network could be regulated through multiple mechanisms to modulate iron storage in various signaling pathways, the deregulation of which results in PCa development and progression.

Ferritin in Kidney and Vascular Related Diseases: Novel Roles for an Old Player

Iron is at the forefront of a number of pivotal biological processes due to its ability to readily accept and donate electrons. However, this property may also catalyze the generation of free radicals with ensuing cellular and tissue toxicity. Accordingly, throughout evolution numerous pathways and proteins have evolved to minimize the potential hazardous effects of iron cations and yet allow for readily available iron cations in a wide variety of fundamental metabolic processes. One of the extensively studied proteins in the context of systemic and cellular iron metabolisms is ferritin. While clinicians utilize serum ferritin to monitor body iron stores and inflammation, it is important to note that the vast majority of ferritin is located intracellularly. Intracellular ferritin is made of two different subunits (heavy and light chain) and plays an imperative role as a safe iron depot. In the past couple of decades our understanding of ferritin biology has remarkably improved. Additionally, a significant body of evidence has emerged describing the significance of the kidney in iron trafficking and homeostasis. Here, we briefly discuss some of the most important findings that relate to the role of iron and ferritin heavy chain in the context of kidney-related diseases and, in particular, vascular calcification, which is a frequent complication of chronic kidney disease.

FTH1P3, a Novel H-Ferritin Pseudogene Transcriptionally Active, Is Ubiquitously Expressed and Regulated during Cell Differentiation

Ferritin, the major iron storage protein, performs its essential functions in the cytoplasm, nucleus and mitochondria. The variable assembly of 24 subunits of the Heavy (H) and Light (L) type composes the cytoplasmic molecule. In humans, two distinct genes code these subunits, both belonging to complex multigene families. Until now, one H gene has been identified with the coding sequence interrupted by three introns and more than 20 intronless copies widely dispersed on different chromosomes. Two of the intronless genes are actively transcribed in a tissue-specific manner. Herein, we report that FTH1P3, another intronless pseudogene, is transcribed. FTH1P3 transcript was detected in several cell lines and tissues, suggesting that its transcription is ubiquitary, as it happens for the parental ferritin H gene. Moreover, FTH1P3 expression is positively regulated during the cell differentiation process.

Hyperferritinaemia-cataract syndrome: worldwide mutations and phenotype of an increasingly diagnosed genetic disorder

The hereditary hyperferritinaemia-cataract syndrome (HHCS) is characterised by an autosomal dominant cataract and high levels of serum ferritin without iron overload. The cataract develops due to L-ferritin deposits in the lens and its pulverulent aspect is pathognomonic. The syndrome is caused by mutations within the iron-responsive element of L-ferritin. These mutations prevent efficient binding of iron regulatory proteins 1 and 2 to the IRE in L-ferritin mRNA, resulting in an unleashed ferritin translation. This paper reviews all 31 mutations (27 single nucleotide transitions and four deletions) that have been described since 1995. Laboratory test showing hyperferritinaemia, normal serum iron and normal transferrin saturation are indicative for HHCS after exclusion of other causes of increased ferritin levels (inflammation, malignancy, alcoholic liver disease) and should prompt an ophthalmological consultation for diagnostic confirmation. Invasive diagnostics such as liver biopsy are not indicated. HHCS is an important differential diagnosis of hyperferritinaemia. Haematologists, gastroenterologists and ophthalmologists should be aware of this syndrome to spare patients from further invasive diagnosis (liver biopsy), and also from a false diagnosis of hereditary haemochromatosis followed by venesections. Patients diagnosed with HHCS should be counselled regarding the relative harmlessness of this genetic disease, with early cataract surgery as the only clinical consequence.

Transferrin and ferritin response to bacterial infection: the role of the liver and brain in fish

Iron is essential for growth and survival, but it is also toxic when in excess. Thus, there is a tight regulation of iron that is accomplished by the interaction of several genes including the iron transporter transferrin and iron storage protein ferritin. These genes are also known to be involved in response to infection. The aim of this study was to understand the role of transferrin and ferritin in infection and iron metabolism in fish. Thus, sea bass transferrin and ferritin H cDNAs were isolated from liver, cloned and characterized. Transferrin constitutive expression was found to be highest in the liver, but also with significant expression in the brain, particularly in the highly vascularized region connecting the inferior lobe of the hypothalamus and the saccus vasculosus. Ferritin, on the other hand, was expressed in all tested organs, but also significantly higher in the liver. Fish were subjected to either experimental bacterial infection or iron modulation and transferrin and ferritin mRNA expression levels were analyzed, along with several iron regulatory parameters. Transferrin expression was found to decrease in the liver and increase in the brain in response to infection and to increase in the liver in iron deficiency. Ferritin expression was found to inversely reflect transferrin in the liver, increasing in infection and iron overload and decreasing in iron deficiency, whereas in the brain, ferritin expression was also increased in infection. These findings demonstrate the evolutionary conservation of transferrin and ferritin dual functions in vertebrates, being involved in both the immune response and iron metabolism.

A general map of iron metabolism and tissue-specific subnetworks

Iron is required for survival of mammalian cells. Recently, understanding of iron metabolism and trafficking has increased dramatically, revealing a complex, interacting network largely unknown just a few years ago. This provides an excellent model for systems biology development and analysis. The first step in such an analysis is the construction of a structural network of iron metabolism, which we present here. This network was created using CellDesigner version 3.5.2 and includes reactions occurring in mammalian cells of numerous tissue types. The iron metabolic network contains 151 chemical species and 107 reactions and transport steps. Starting from this general model, we construct iron networks for specific tissues and cells that are fundamental to maintaining body iron homeostasis. We include subnetworks for cells of the intestine and liver, tissues important in iron uptake and storage, respectively, as well as the reticulocyte and macrophage, key cells in iron utilization and recycling. The addition of kinetic information to our structural network will permit the simulation of iron metabolism in different tissues as well as in health and disease.

A duplication at chromosome 11q12.2-11q12.3 is associated with spinocerebellar ataxia type 20

Spinocerebellar ataxia type 20 (SCA20) has been linked to chromosome 11q12, but the underlying genetic defect has yet to be identified. We applied single-nucleotide polymorphism genotyping to detect structural alterations in the genomic DNA of patients with SCA20. We found a 260 kb duplication within the previously linked SCA20 region, which was confirmed by quantitative polymerase chain reaction and fiber fluorescence in situ hybridization, the latter also showing its direct orientation. The duplication spans 10 known and 2 unknown genes, and is present in all affected individuals in the single reported SCA20 pedigree. While the mechanism whereby this duplication may be pathogenic remains to be established, we speculate that the critical gene within the duplicated segment may be DAGLA, the product of which is normally present at the base of Purkinje cell dendritic spines and contributes to the modulation of parallel fiber-Purkinje cell synapses.

Screening and cloning of genes coding for leukocyte proteins interacting with NS5ATP9 by yeast-two hybrid technique

AIM: To investigate the biological functions of NS5ATP9, and to screen proteins in leukocytes interacting NS5ATP9 protein by yeast-two hybrid.

METHODS: The NS5ATP9 gene was amplified by polymerase chain reaction (PCR) and NS5ATP9 bait plasmid was constructed by using yeast-two hybrid system 3, and the yeast AH109 was then transformed. The transformed yeast mated with yeast Y187 containing leukocytes cDNA library plasmid in 2×YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) and synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing X--gal for selecting two times and screening. After extracting and sequencing of plasmid DNA from blue colonies, we underwent analysis by bioinformatics.

RESULTS: Forty six colonies were sequenced, among which thirteen colonies were Homo sapiens immunoglobulin light chain, ten ubiquitin, two ferritin heavy chain, eleven Homo sapiens rearranged immunoglobulin lambda light chain, one 14-3-3 family protein, one Meningococcus PorA protein, three RNA polymerase III, one tobacco mitogen activated protein kinase, two cytochrome P450 II, one SLIT2 protein, and one dependent-protein kinase catalylic subunit.

CONCLUSION: Genes of NS5ATP9 interacting proteins in leukocytes are successfully cloned and the results bring some new clues for studying the biological functions of NS5ATP9 and associated proteins.

Genetic or pharmacological iron chelation prevents MPTP-induced neurotoxicity in vivo: a novel therapy for Parkinson's disease

Studies on postmortem brains from Parkinson's patients reveal elevated iron in the substantia nigra (SN). Selective cell death in this brain region is associated with oxidative stress, which may be exacerbated by the presence of excess iron. Whether iron plays a causative role in cell death, however, is controversial. Here, we explore the effects of iron chelation via either transgenic expression of the iron binding protein ferritin or oral administration of the bioavailable metal chelator clioquinol (CQ) on susceptibility to the Parkinson's-inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrapyridine (MPTP). Reduction in reactive iron by either genetic or pharmacological means was found to be well tolerated in animals in our studies and to result in protection against the toxin, suggesting that iron chelation may be an effective therapy for prevention and treatment of the disease.

Comprehensive hereditary hemochromatosis genotyping

Hereditary hemochromatosis (HH) is an iron-overload disease common in populations of Northern European origin. Patients display increased iron absorption leading to excessive iron deposition and potential multiorgan failure. Using polymerase chain reaction sequence-specific primer (PCR-SSP) technology, we have developed an HH diagnosis assay capable of detecting 19 non-synonymous HFE mutations (including a previously unreported mutation, V295A) and several TFR2, SLC11A3 and H ferritin alleles implicated in HH. As part of the validation process, 159 UK renal donors were genotyped to determine HH allele frequencies in the UK population. The alleles nominally identified as HFE*01 (C282Y), HFE*02 (H63D) and HFE*03 (S65C) were found at frequencies of 0.085, 0.173 and 0.009, respectively. All other potential HH-associated alleles were absent, confirming their low prevalence in this population. This assay enables comprehensive routine HH genotyping, producing rapid, accurate and reproducible results at low cost.

Cloning and sequence analysis of cDNA for heavy-chain ferritin from the Canis familiaris

Ferritin serves as a storage protein for iron in animals. Complementary DNA encoding a heavy chain ferritin was cloned from the brain of Canis familiaris. The dog ferritin cDNA encodes a 182 amino acid that shows high levels of amino acid identity with vertebrate ferritins (90-98%). Near the cap region of the 5'-untranslated region, the dog H-ferritin mRNA displays a 28-nucleotide sequence that is exactly conserved in the corresponding region of the human and pig H-ferritin mRNA, thus making this sequence a prime candidate for involvement in the known translational regulation of H-ferritin by iron.

Specific repression of beta-globin promoter activity by nuclear ferritin

Developmental hemoglobin switching involves sequential globin gene activations and repressions that are incompletely understood. Earlier observations, described herein, led us to hypothesize that nuclear ferritin is a repressor of the adult beta-globin gene in embryonic erythroid cells. Our data show that a ferritin-family protein in K562 cell nuclear extracts binds specifically to a highly conserved CAGTGC motif in the beta-globin promoter at -153 to -148 bp from the cap site, and mutation of the CAGTGC motif reduces binding 20-fold in competition gel-shift assays. Purified human ferritin that is enriched in ferritin-H chains also binds the CAGTGC promoter segment. Expression clones of ferritin-H markedly repress beta-globin promoter-driven reporter gene expression in cotransfected CV-1 cells in which the beta-promoter has been stimulated with the transcription activator erythroid Krüppel-like factor (EKLF). We have constructed chloramphenicol acetyltransferase reporter plasmids containing either a wild-type or mutant beta-globin promoter for the -150 CAGTGC motif and have compared the constructs for susceptibility to repression by ferritin-H in cotransfection assays. We find that stimulation by cotransfected EKLF is retained with the mutant promoter, whereas repression by ferritin-H is lost. Thus, mutation of the -150 CAGTGC motif not only markedly reduces in vitro binding of nuclear ferritin but also abrogates the ability of expressed ferritin-H to repress this promoter in our cell transfection assay, providing a strong link between DNA binding and function, and strong support for our proposal that nuclear ferritin-H is a repressor of the human beta-globin gene. Such a repressor could be helpful in treating sickle cell and other genetic diseases.

A mutation, in the iron-responsive element of H ferritin mRNA, causing autosomal dominant iron overload

Ferritin, which is composed of H and L subunits, plays an important role in iron storage and in the control of intracellular iron distribution. Synthesis of both ferritin subunits is controlled by a common cytosolic protein, iron regulatory protein (IRP), which binds to the iron-responsive element (IRE) in the 5'-UTR of the H- and L-ferritin mRNAs. In the present study, we have identified a single point mutation (A49U) in the IRE motif of H-ferritin mRNA, in four of seven members of a Japanese family affected by dominantly inherited iron overload. Gel-shift mobility assay and Scatchard-plot analysis revealed that a mutated IRE probe had a higher binding affinity to IRP than did the wild-type probe. When mutated H subunit was overexpressed in COS-1 cells, suppression of H-subunit synthesis and of the increment of radiolabeled iron uptake were observed. These data suggest that the A49U mutation in the IRE of H-subunit is responsible for tissue iron deposition and is a novel cause of hereditary iron overload, most likely related to impairment of the ferroxidase activity generated by H subunit.

Structure and location of a ferritin gene of the yellow fever mosquito Aedes aegypti

We have isolated and sequenced a genomic clone encoding the 24- and 26-kDa ferritin subunits in the mosquito Aedes aegypti (Rockefeller strain). The A. aegypti gene differs from other known ferritin genes in that it possesses an additional intron and an unusually large second intron. The additional intron is located within the 5' untranslated region, between the CAP site and the start codon. The second intron contains numerous putative transposable elements. In addition, unlike the human and rat ferritin genes, the A. aegypti ferritin gene is a single copy gene, located at 88.3% FLpter on the q-arm of chromosome 1. Primer extension analysis indicates that the A. aegypti ferritin gene has multiple transcriptional start sites. A differential usage of these sites is observed with varied cellular iron concentrations.

Organization of the ferritin genes in Drosophila melanogaster

The organization of two closely clustered genes, Fer1HCH and Fer2LCH, encoding the heavy-chain homolog (HCH) and the light-chain homolog (LCH) subunits of Drosophila melanogaster ferritin are reported here. The 5019-bp sequence of the cluster was assembled from genomic fragments obtained by polymerase chain reaction (PCR) amplification of genomic DNA and from sequences obtained from the Berkeley Drosophila Genome Project (BDGP) (http://www.fruitfly.org). These genes, located at position 99F1, have different exon-intron structures (Fer1HCH has three introns and Fer2LCH has two introns) and are divergently transcribed. Computer analysis of the possibly shared promoter regions revealed the presence of putative metal regulatory elements (MREs), a finding consistent with the upregulation of these genes by iron, and putative NF-kappaB-like binding sites. The structure of two other invertebrate ferritin genes, from the nematode Caenorhabditis elegans (located on chromosomes I and V), was also analyzed. Both nematode genes have two introns, lack iron-responsive elements (IREs), and encode ferritin subunits similar to vertebrate H chains. These findings, along with comparisons of ferritin genes from invertebrates, vertebrates, and plants, suggest that the specialization of ferritin H and L type chains, the complex exon-intron organization of plant and vertebrate genes, and the use of the IRE/iron regulatory protein (IRP) mechanism for regulation of ferritin synthesis are recent evolutionary acquisitions.

Coordinated regulation of iron-controlling genes, H-ferritin and IRP2, by c-MYC

The protein encoded by the c-MYC proto-oncogene is a transcription factor that can both activate and repress the expression of target genes, but few of its transcriptional targets have been identified. Here, c-MYC is shown to repress the expression of the heavy subunit of the protein ferritin (H-ferritin), which sequesters intracellular iron, and to stimulate the expression of the iron regulatory protein-2 (IRP2), which increases the intracellular iron pool. Down-regulation of the expression of H-ferritin gene was required for cell transformation by c-MYC. These results indicate that c-MYC coordinately regulates genes controlling intracellular iron concentrations and that this function is essential for the control of cell proliferation and transformation by c-MYC.

Genetic mapping of the mouse ferritin light chain gene and 11 pseudogenes on 11 mouse chromosomes

We typed the progeny of two sets of genetic crosses to determine the map locations for loci containing sequences related to the ferritin light chain (Ft11) gene. Twelve loci were positioned on 11 different chromosomes. One of these genes mapped to a position on Chr 7 predicted to contain the expressed gene on the basis of the previously determined position of the human homolog on 19q13.3-q13.4.

A gene map of the Best's vitelliform macular dystrophy region in chromosome 11q12-q13.1

Best's vitelliform macular dystrophy is an autosomal dominant disorder of unknown causes. To identify the underlying gene defect the disease locus has been mapped to an approximately 1.4-Mb region on chromosome 11q12-q13.1. As a prerequisite for its positional cloning we have assembled a high coverage PAC contig of the candidate region. Here, we report the construction of a primary transcript map that places a total of 19 genes within the Best's disease region. This includes 14 transcripts of as yet unknown function obtained by EST mapping and/or cDNA selection and five genes mapped previously to the interval (CD5, PGA, DDB1, FEN1, and FTH1). Northern blot analyses were performed to determine the expression profiles in various human tissues. At least three genes appear to be good candidates for Best's disease based on their abundant expression in retina or retinal pigment epithelium. Additional information on the functional properties of these genes, as well as mutation analyses in Best's disease patients, have to await their further characterization. [The GenBank/EMBL accession numbers and details of the isolation, localization, and characterization of ESTs and selected cDNAs are available as online supplements in Online Tables 1-3 at http://www.genome.org.]

Regulation of expression of ferritin H-chain and transferrin receptor by protoporphyrin IX

The effect of protoporphyrin IX (hemin without iron) on the expression of transferrin receptor and ferritin was investigated in Friend leukemia cells. Cells treated with protoporphyrin IX exhibit enhanced transferrin-receptor expression and markedly reduced ferritin synthesis. Stimulation of transferrin-receptor expression is observed at both the mRNA and protein level. The effect on ferritin synthesis is mediated by translational inhibition of the mRNA, which, in contrast, is transcriptionally stimulated by protoporphyrin IX treatment. The regulation of transferrin receptor and ferritin in response to iron perturbations has been studied extensively and is mediated by the binding of iron-regulatory proteins (IRP) to the iron-responsive elements (IRE) present in the 3' and 5' untranslated regions of the transferrin-receptor and ferritin mRNA, respectively. To elucidate the molecular mechanisms underlying the effects of protoporphyrin IX on ferritin and transferrin-receptor expression, the role of the IRE sequence was investigated both in vivo by transfection experiments, with a construct containing the coding region for the chloramphenicol acetyltransferase (CAT) reporter gene under the translational control of the ferritin IRE, and in vitro by RNA band-shift assays. Whereas, examination of IRP binding to the IRE by in vitro assays suggests an apparent inactivation of IRP by protoporphyrin IX treatment, CAT assays indicate that protoporphyrin IX is able to induce in vivo a translational inhibition similar to that obtained by treatment with the iron chelator Desferal. This observation raises the possibility of different effects on the IRP activity exerted by porphyrin treatment in intact tissue-culture cells and in vitro. We conclude that translation of ferritin mRNA and degradation of transferrin-receptor mRNA are inhibited in intact tissue-culture cells by protoporphyrin IX through a mechanism similar to that exerted by iron chelation, thus involving depletion of the intracellular iron pool. These results can improve the understanding of the regulation of ferritin gene expression in some pathological conditions associated with disturbed heme synthesis.

Conserved mutations in human ferritin H pseudogenes: a second functional sequence or an evolutionary quirk?

This paper describes a search for a second functional human ferritin H gene in a collection of genomic clones. Nine new H-like sequences have been mapped to chromosomes 1p22-31, 1q32-42, 2q32-33, 3q21-23, 13q12, 14, 17p11-pter and X. These were examined for evidence of possible functionality by sequencing and by searching for possible introns. All except an uncharacterized sequence on chromosome 13 appear to be processed pseudogenes. However, nearly all share several conserved differences with the known functional sequence. These differences occur at regions of unusual structure. It is not known whether these sequences are derived from a second functional gene or from site-specific mutations in the generation of pseudogenes from the known functional gene. We also show that several hominoids contain H gene families with similar complexities to humans and that most of the human genes have counterparts in chimpanzees and gorillas.

Transcriptional regulation of the ferritin heavy-chain gene: the activity of the CCAAT binding factor NF-Y is modulated in heme-treated Friend leukemia cells and during monocyte-to-macrophage differentiation

The ferritin H-chain gene promoter regulation was analyzed in heme-treated Friend leukemia cells (FLCs) and during monocyte-to-macrophage differentiation. In the majority of cell lines studied, the regulation of ferritin expression was exerted mostly at the translational level. However, in differentiating erythroid cells, which must incorporate high levels of iron to sustain hemoglobin synthesis, and in macrophages, which are involved in iron storage, transcriptional regulation seemed to be a relevant mechanism. We show here that the minimum region of the ferritin H-gene promoter that is able to confer transcriptional regulation by heme in FLCs to a reporter gene is 77 nucleotides upstream of the TATA box. This cis element binds a protein complex referred to as HRF (heme-responsive factor), which is greatly enhanced both in heme-treated FLCs and during monocyte-to-macrophage differentiation. The CCAAT element present in reverse orientation in this promoter region of the ferritin H-chain gene is necessary for binding and for gene activity, since a single point mutation is able to abolish the binding of HRF and the transcriptional activity in transfected cells. By competition experiments and supershift assays, we identified the induced HRF as containing at least the ubiquitous transcription factor NF-Y. NF-Y is formed by three subunits, A, B, and C, all of which are necessary for DNA binding. Cotransfection with a transdominant negative mutant of the NF-YA subunit abolishes the transcriptional activation by heme, indicating that NF-Y plays an essential role in this activation. We have also observed a differential expression of the NF-YA subunit in heme-treated and control FLCs and during monocyte-to-macrophage differentiation.

Structure and differential expression of two maize ferritin genes in response to iron and abscisic acid

In plants, synthesis of the iron-storage protein ferritin in response to iron is not regulated at the translational level; this is in contrast to ferritin synthesis in animals. Part of the response is mediated through a transduction pathway which involves the plant hormone abscisic acid. In this work, we report the cloning and sequencing of two maize ferritin genes (ZmFer1 and ZmFer2) coding for members of the two ferritin mRNA subclasses, FM1 and FM2, respectively. Although plant and animal ferritins are closely related proteins, a major difference is observed between the organisation of the genes. Both maize ferritin genes are organised as eight exons and seven introns, the positions of which are identical within the two genes, while animal ferritin genes are interrupted by three introns, at positions different from those found in maize genes. Sequence divergence between the 3' untranslated regions of these genes has allowed the use of specific probes to study the accumulation of FM1 and FM2 transcripts in response to various environmental cues. Such probes have shown that FM1 and FM2 transcripts accumulate with differential kinetics in response to iron; FM1 mRNA accumulate earlier than FM2 mRNA and only FM2 transcripts accumulate in response to exogenous abscisic acid or water stress. Mapping of the transcriptional initiation region of these two genes defined their 5' upstream regions and allowed a sequence comparison of their promoters, which appeared highly divergent. This raises the possibility that the differential accumulation of FM1 and FM2 mRNAs in response to iron, abscisic acid and drought could be due to differential transcription of ZmFer1 and ZmFer2.

Localization of a new ferritin heavy chain sequence present in human brain mRNA to chromosome 11

Two types of ferritin heavy (H) chain clones have been isolated from cDNA libraries of human fetal and adult brain: one corresponds to the ferritin H chain mRNA that is abundant in liver and is called "liver-like" brain cDNA; the other contains an additional 279 nucleotide (nt) sequence in the 3' untranslated region and is called brain ferritin H chain cDNA. To map the 279-nt sequence, polymerase chain reaction (PCR) amplification was carried out using DNA from rodent x human hybrid cell lines containing single human chromosomes as templates, and oligomeric primers homologous to the 3' end of the 279-nt sequence (primer A) and to a coding sequence just 5' to the 279-nt sequence. Significant PCR product of the size expected from analysis of the brain ferritin H chain cDNA clones and a genomic ferritin H chain clone (487 bp) was generated only from hybrid-cell DNA containing human chromosome 11. This PCR product and the "liver-like" brain cDNA (lacking the 279-nt sequence) both hybridized to chromosome 11 fragments that are known to define the well-characterized functional liver ferritin H chain gene and a putative pseudogene. Preliminary data indicate that primer A (and thus the 279-nt sequence) maps to the functional ferritin H chain gene fragments, but binding to the pseudogene has not been ruled out.

Proteins binding to 5' untranslated region sites: a general mechanism for translational regulation of mRNAs in human and yeast cells

We demonstrate that a bacteriophage protein and a spliceosomal protein can be converted into eukaryotic translational repressor proteins. mRNAs with binding sites for the bacteriophage MS2 coat protein or the spliceosomal human U1A protein were expressed in human HeLa cells and yeast. The presence of the appropriate binding protein resulted in specific, dose-dependent translational repression when the binding sites were located in the 5' untranslated region (UTR) of the reporter mRNAs. Neither mRNA export from the nucleus to the cytoplasm nor mRNA stability was demonstrably affected by the binding proteins. The data thus reveal a general mechanism for translational regulation: formation of mRNA-protein complexes in the 5' UTR controls translation initiation by steric blockage of a sensitive step in the initiation pathway. Moreover, the findings establish the basis for novel strategies to study RNA-protein interactions in vivo and to clone RNA-binding proteins.

Proteins binding to 5' untranslated region sites: a general mechanism for translational regulation of mRNAs in human and yeast cells

We demonstrate that a bacteriophage protein and a spliceosomal protein can be converted into eukaryotic translational repressor proteins. mRNAs with binding sites for the bacteriophage MS2 coat protein or the spliceosomal human U1A protein were expressed in human HeLa cells and yeast. The presence of the appropriate binding protein resulted in specific, dose-dependent translational repression when the binding sites were located in the 5' untranslated region (UTR) of the reporter mRNAs. Neither mRNA export from the nucleus to the cytoplasm nor mRNA stability was demonstrably affected by the binding proteins. The data thus reveal a general mechanism for translational regulation: formation of mRNA-protein complexes in the 5' UTR controls translation initiation by steric blockage of a sensitive step in the initiation pathway. Moreover, the findings establish the basis for novel strategies to study RNA-protein interactions in vivo and to clone RNA-binding proteins.

The interaction between the iron-responsive element binding protein and its cognate RNA is highly dependent upon both RNA sequence and structure

To assess the influence of RNA sequence/structure on the interaction RNAs with the iron-responsive element binding protein (IRE-BP), twenty eight altered RNAs were tested as competitors for an RNA corresponding to the ferritin H chain IRE. All changes in the loop of the predicted IRE hairpin and in the unpaired cytosine residue characteristically found in IRE stems significantly decreased the apparent affinity of the RNA for the IRE-BP. Similarly, alteration in the spacing and/or orientation of the loop and the unpaired cytosine of the stem by either increasing or decreasing the number of base pairs separating them significantly reduced efficacy as a competitor. It is inferred that the IRE-BP forms multiple contacts with its cognate RNA, and that these contacts, acting in concert, provide the basis for the high affinity of this interaction.

Pathogenesis of genetic haemochromatosis

Genetic haemochromatosis is an autosomal recessive inherited iron overload disease. The genetic defect and the underlying metabolic error are not known. Several observations indicate that the 2-4-fold increase of iron absorption is due to a regulatory defect of a membrane iron transport system in duodenal mucosal cells. The key pathophysiologic factor may be the increase of gut-derived non-transferrin bound iron liganded to low-molecular mass organic molecules. A putative membrane carrier protein for non-transferrin bound iron was identified and preliminary data suggest its enrichment in plasma membranes of human mucosal cells as well as in liver and other organs which are affected in genetic haemochromatosis. Cellular accumulation of ionic iron leads to peroxidative decomposition of organelle membrane phospholipids with the consequence of cell degeneration and cell death. Impairment of organ function and structural alterations such as cirrhosis of the liver are clinical manifestations.

The ferritin genes: their response to iron status

Iron is a required nutrient which, at high concentrations, can peroxidize cell lipids and other cellular components. To prevent excess iron from damaging cells, it is stored in ferritin, which consists of a shell of protein subunits of two related types, H (heavy) and L (light), surrounding a cavity in which the iron can be deposited. In order to prepare for a rapid increase in ferritin in response to a rise in cellular iron, a large number of dormant ferritin mRNAs are accumulated in the cytoplasm. These can be rapidly activated to yield a large population of ferritin subunits. Regulation is achieved through a 28-nucleotide "stem-and-loop" structure near the beginning of the H- and L-ferritin mRNAs. When this structure is associated with a binding protein (iron regulatory element binding protein, IRE-BP), translation of the ferritin mRNA cannot proceed. However, when intracellular iron accumulates, IRE-BP releases its hold and translation of the mRNA then takes place. IRE-BP has been identified as a cytosolic form of aconitase, containing several fourfold iron-sulfur clusters. Within each cluster one iron atom is labile; this may be the mechanism by which IRE-BP responds to intracellular iron levels. Finally, transcription of the L- and H-genes shows that L is preferentially transcribed in response to increased iron intake, whereas H responds to cell differentiation and other factors. More work is needed to define independent transcription of the individual genes, including regulation of components other than the 28-nucleotide segment.

Modulation of ferritin H-chain expression in Friend erythroleukemia cells: transcriptional and translational regulation by hemin

The mechanisms that regulate the expression of the H chain of the iron storage protein ferritin in Friend erythroleukemia cells (FLCs) after exposure to hemin (ferric protoporphyrin IX), protoporphyrin IX, and ferric ammonium citrate (FAC) have been investigated. Administration of hemin increases the steady-state level of ferritin mRNA about 10-fold and that of ferritin protein expression 20-fold. Experiments with the transcriptional inhibitor actinomycin D and transfection studies demonstrate that the increment in cytoplasmic mRNA content results from enhanced transcription of the ferritin H-chain gene and cannot be attributed to stabilization of preexisting mRNAs. In addition to transcriptional effects, translational regulation induces the recruitment of stored mRNAs into functional polyribosomes after hemin and FAC administration, resulting in a further increase in ferritin synthesis. Administration of protoporphyrin IX to FLCs produces divergent transcriptional and translational effects. It increases transcription but appears to suppress ferritin mRNA translation. FAC treatment increases the mRNA content slightly (about twofold), and the ferritin levels rise about fivefold over the control values. We conclude that in FLCs, hemin induces ferritin H-chain biosynthesis by multiple mechanisms: a transcriptional mechanism exerted also by protoporphyrin IX and a translational one, not displayed by protoporphyrin IX but shared with FAC.

Modulation of ferritin H-chain expression in Friend erythroleukemia cells: transcriptional and translational regulation by hemin

The mechanisms that regulate the expression of the H chain of the iron storage protein ferritin in Friend erythroleukemia cells (FLCs) after exposure to hemin (ferric protoporphyrin IX), protoporphyrin IX, and ferric ammonium citrate (FAC) have been investigated. Administration of hemin increases the steady-state level of ferritin mRNA about 10-fold and that of ferritin protein expression 20-fold. Experiments with the transcriptional inhibitor actinomycin D and transfection studies demonstrate that the increment in cytoplasmic mRNA content results from enhanced transcription of the ferritin H-chain gene and cannot be attributed to stabilization of preexisting mRNAs. In addition to transcriptional effects, translational regulation induces the recruitment of stored mRNAs into functional polyribosomes after hemin and FAC administration, resulting in a further increase in ferritin synthesis. Administration of protoporphyrin IX to FLCs produces divergent transcriptional and translational effects. It increases transcription but appears to suppress ferritin mRNA translation. FAC treatment increases the mRNA content slightly (about twofold), and the ferritin levels rise about fivefold over the control values. We conclude that in FLCs, hemin induces ferritin H-chain biosynthesis by multiple mechanisms: a transcriptional mechanism exerted also by protoporphyrin IX and a translational one, not displayed by protoporphyrin IX but shared with FAC.

Position is the critical determinant for function of iron-responsive elements as translational regulators

At least two groups of eukaryotic mRNAs (ferritin and erythroid 5-aminolevulinate synthase) are translationally regulated via iron-responsive elements (IREs) located in a conserved position within the 5' untranslated regions of their mRNAs. We establish that the spacing between the 5' terminus of an mRNA and the IRE determines the potential of the IRE to mediate iron-dependent translational repression. The length of the RNA spacer rather than its nucleotide sequence or predicted secondary structure is shown to be the primary determinant of IRE function. When the position of the IRE is preserved, sequences flanking the IRE in natural ferritin mRNA can be replaced by altered flanking sequences without affecting the regulatory function of the IRE in vivo. These results define position as a critical cis requirement for IRE function in vivo and imply the potential to utilize transcription start site selection to modulate the function of this translational regulator.

Position is the critical determinant for function of iron-responsive elements as translational regulators

At least two groups of eukaryotic mRNAs (ferritin and erythroid 5-aminolevulinate synthase) are translationally regulated via iron-responsive elements (IREs) located in a conserved position within the 5' untranslated regions of their mRNAs. We establish that the spacing between the 5' terminus of an mRNA and the IRE determines the potential of the IRE to mediate iron-dependent translational repression. The length of the RNA spacer rather than its nucleotide sequence or predicted secondary structure is shown to be the primary determinant of IRE function. When the position of the IRE is preserved, sequences flanking the IRE in natural ferritin mRNA can be replaced by altered flanking sequences without affecting the regulatory function of the IRE in vivo. These results define position as a critical cis requirement for IRE function in vivo and imply the potential to utilize transcription start site selection to modulate the function of this translational regulator.

A second ferritin L subunit is encoded by an intronless gene in the mouse

Multiple homologous sequences for the ferritin L subunit are present in mammalian genomes, but so far, only one expressed gene has been described. Here we report the isolation of a cDNA from a mouse bone marrow library, corresponding to an isoform of the mouse ferritin L subunit. This new subunit, that we named Lg, differs from the L subunit of ten amino acids. Specific amplification of mouse genomic DNA using the polymerase chain reaction (PCR) confirmed the presence of this Lg sequence in the mouse genome but also suggested that it must be encoded by an intronless gene. Using a series of different Lg-specific oligonucleotides as probes, we subsequently isolated a genomic clone containing an uninterrupted sequence, identical to the Lg cDNA. This Lg gene lacks introns and does not contain the 28 base pairs (bp) conserved motif usually present at the 5' end of most ferritin mRNAs, which confers translational regulation by iron. When transiently transfected into K562 cells, this Lg genomic clone is actively transcribed, suggesting that, although it possesses the characteristics of a processed pseudogene, it is likely to correspond to the gene encoding this new ferritin subunit.

Polymorphism in a ferritin H gene from chromosome 6p

This paper addresses the question of whether abnormalities in ferritin expression in the iron storage disease hemochromatosis (HC) involve major deletions or alterations in regions containing the two ferritin H genes that lie near the disease locus on chromosome 6p. We present evidence from analyses of Southern blots that neither gene is deleted in hemochromatosis. We also describe a polymorphism in one of the genes that we have previously shown to be a processed pseudogene. This polymorphism does not correlate with the presence of HC. The PIC value for this polymorphism was calculated as 0.49.

Ferritin immunohistochemistry as a marker for microglia

An immunohistochemical analysis of formalin-fixed, paraffin-embedded brain sections was performed with antisera against holoferritin and the light(L)-subunit of ferritin. Sections immunostained using anti-glial fibrillary acidic protein (GFAP), Ricinus communis agglutinin-1 (RCA-1) stain for microglia and iron stain (Berlin blue stain) were compared. The L-subunit of ferritin was purified from normal human spleen according to the modified scrapie-associated fibrils purification, and the anti-serum was raised in a rabbit. Both ferritin antisera positively stained resting and, more markedly, reactive microglia, both of which were also stained with RCA-1 but not with GFAP. Ferritin-positive resting microglia were seen more abundantly in cerebral and cerebellar cortices than in white matter. The advantages of ferritin antisera over RCA-1 are as follows. (1) RCA-1 heavily stains blood vessels, while anti-ferritin does not, hence the microglial cells are more readily visualized with ferritin immunohistochemistry. (2) Reactive microglia and macrophages are more strongly stained with anti-ferritin. (3) The staining intensity of ferritin is independent of the length of tissue fixation in formalin. However, anti-ferritin is inferior to RCA-1 in staining resting microglia with a scanty cytoplasm, especially in the white matter, probably because the former recognizes cytoplasmic components, while the latter recognizes cell membrane. Iron stain only gave a reaction to microglial cells in brains with neurosyphilis and to hemosiderin-laden macrophages. Thus, in addition to RCA-1, ferritin antisera are useful as a microglia marker in formalin-fixed, paraffin-embedded sections.

A fine-structure deletion map of human chromosome 11p: analysis of J1 series hybrids

Deletion analysis offers a powerful alternative to linkage and karyotypic approaches for human chromosome mapping. A panel of deletion hybrids has been derived by mutagenizing J1, a hamster cell line that stably retains chromosome 11 as its only human DNA, and selecting for loss of MIC1, a surface antigen encoded by a gene in band 11p13. A unique, self-consistent map was constructed by analyzing the pattern of marker segregation in 22 derivative cells lines; these carry overlapping deletions of 11p13, but selectively retain a segment near the 11p telomere. The map orders 35 breakpoints and 36 genetic markers, including 3 antigens, 2 isozymes, 12 cloned genes, and 19 anonymous DNA probes. The deletions span the entire short arm, dividing it into more than 20 segments and define a set of reagents that can be used to rapidly locate any newly identified marker on 11p, with greatest resolution in the region surrounding MIC1. The approach we demonstrate can be applied to map any mammalian chromosome. To test the gene order, we examined somatic cell hybrids from five patients, whose reciprocal translocations bisect band 11p13; these include two translocations associated with familial aniridia and two with acute T-cell leukemia. In each patient, the markers segregate in telomeric and centromeric groups as predicted by the deletion map. These data locate the aniridia gene (AN2) and a recurrent T-cell leukemia breakpoint (TCL2) in the marker sequence, on opposite sides of MIC1. To provide additional support, we have characterized the dosage of DNA markers in a patient with Beckwith-Wiedemann syndrome and an 11p15-11pter duplication. Our findings suggest the following gene order: TEL - (HRAS1, MER2, CTSD, TH/INS/IGF2, H19, D11S32) - (RRM1, D11S1, D11S25, D11S26) - D11S12 - (HBBC, D11S30) - D11S20 - (PTH, CALC) - (LDHA, SAA, TRPH, D11S18, D11S21) - D11S31 - D11S17 - HBVS1 - (FSHB, D11S16) - AN2 - MIC1 - TCL2 - delta J - CAT - MIC4 - D11S9 - D11S14 - ACP2 - (D11S33, 14L) - CEN. We have used the deletion map to show the distribution on 11p of two centromeric repetitive elements and the low-order interspersed repeat A36Fc. Finally, we provide evidence for an allelic segregation event in the hamster genome that underlies the stability of chromosome 11 in J1. The deletion map provides a basis to position hereditary disease loci on 11p, to distinguish the pattern of recessive mutations in different forms of cancer and, since many of these genes have been mapped in other mammalian species, to study the evolution of a conserved syntenic group.

Temporal order of gene replication in Chinese hamster ovary cells

To investigate the molecular basis of the regulatory mechanisms responsible for the orderly replication of the mammalian genome, we have developed an experimental system by which the replication order of various genes can be defined with relative ease and precision. Exponentially growing CHO-K1 cells were separated into populations representing various stages of the cell cycle by centrifugal elutriation and analyzed for cell cycle status flow cytometry. The replication of specific genes in each elutriated fraction was measured by labeling with 5-mercuri-dCTP and [3H]dTPP under conditions of optimal DNA synthesis after cell permeabilization with lysolecithin. Newly synthesized mercurated DNA from each elutriated fraction was purified by affinity chromatography on thiol-agarose and replicated with the large fragment of Escherichia coli DNA polymerase I by using [alpha-32P]dATP and random primers. The 32P-labeled DNA representative of various stages of the cell cycle was then hybridized with dot blots of plasmid DNA containing specific cloned genes. From these results, it was possible to deduce the nuclear DNA content at the time each specific gene replicated during S phase (C value). The C values of 29 genes, which included single-copy genes, multifamily genes, oncogenes, and repetitive sequences, were determined and found to be distributed over the entire S phase. Of the 28 genes studied, 19 had been examined by others using in vivo labeling techniques, with results which agreed with the replication pattern observed in this study. The replication times of nine other genes are described here for the first time. Our method of analysis is sensitive enough to determine the replication time of single-copy genes. The replication times of various genes and their levels of expression in exponentially growing CHO cells were compared. Although there was a general correlation between transcriptional activity and replication in the first half of S phase, examination of specific genes revealed a number of exceptions. Approximately 25% of total poly(A) RNA was transcribed from the late-replicating DNA.

cDNA sequence, gene organization, and progesterone induction of mRNA for uteroferrin, a porcine uterine iron transport protein

The complete nucleotide sequence of porcine uteroferrin mRNA was determined by analysis of overlapping cDNA and genomic clones. The uteroferrin mRNA is 1,424 nucleotides in length and encodes a precursor protein of 338 amino acids, of which 20 residues subsequently are cleaved to form the mature peptide. The uteroferrin gene spans 3.5 kb and consists of three exons and two introns. The first intron separates the 5' untranslated sequences from the translation initiation codon ATG while the other intron interrupts the coding region of the mature protein. Primer extension analysis localized the presumptive transcription initiation site of the mRNA 94 nucleotides 5' of the ATG. No canonical TATA or CAAT sequences were apparent upstream from the mRNA cap site. However, sequences within the 5'-flanking region of the gene exhibit similarities to defined regulatory sequences for iron- and steroid hormone-responsive genes. The steady-state level of uteroferrin mRNA is enhanced by progesterone but not by estrogen alone, although the extent of progesterone induction is lower than at midgestation. The simple organization of the uteroferrin gene, which contrasts with those of the transferrin gene family, and the progesterone induction of uteroferrin mRNA expression suggest that, although this protein may have evolved in a manner distinct from other iron binding proteins, its regulation by steroid hormones may be similar.

Chromosomal localization of nucleic acid-binding proteins by affinity mapping: assignment of the IRE-binding protein gene to human chromosome 9

Three human mRNAs are regulated post-transcriptionally by iron via iron-responsive elements (IREs) contained in each mRNA. A cytoplasmic protein (IRE-BP) binds to these cis-acting elements and mediates the translational regulation of ferritin H- and L-chain mRNA and the iron-dependent stability of transferrin receptor (TfR) mRNA. We have taken advantage of the different mobilities of the human and rodent IRE/IRE-BP complexes on non-denaturing polyacrylamide gels to determine the chromosomal localization of the gene encoding the IRE-BP. Utilizing a panel of 34 different human/rodent hybrid cell lines we have assigned the IRE-BP gene to human chromosome 9. This new technique based on nucleic acid/protein interaction may allow determination of the chromosomal localization of other RNA- or DNA-binding proteins.

Temporal order of gene replication in Chinese hamster ovary cells

To investigate the molecular basis of the regulatory mechanisms responsible for the orderly replication of the mammalian genome, we have developed an experimental system by which the replication order of various genes can be defined with relative ease and precision. Exponentially growing CHO-K1 cells were separated into populations representing various stages of the cell cycle by centrifugal elutriation and analyzed for cell cycle status flow cytometry. The replication of specific genes in each elutriated fraction was measured by labeling with 5-mercuri-dCTP and [3H]dTPP under conditions of optimal DNA synthesis after cell permeabilization with lysolecithin. Newly synthesized mercurated DNA from each elutriated fraction was purified by affinity chromatography on thiol-agarose and replicated with the large fragment of Escherichia coli DNA polymerase I by using [alpha-32P]dATP and random primers. The 32P-labeled DNA representative of various stages of the cell cycle was then hybridized with dot blots of plasmid DNA containing specific cloned genes. From these results, it was possible to deduce the nuclear DNA content at the time each specific gene replicated during S phase (C value). The C values of 29 genes, which included single-copy genes, multifamily genes, oncogenes, and repetitive sequences, were determined and found to be distributed over the entire S phase. Of the 28 genes studied, 19 had been examined by others using in vivo labeling techniques, with results which agreed with the replication pattern observed in this study. The replication times of nine other genes are described here for the first time. Our method of analysis is sensitive enough to determine the replication time of single-copy genes. The replication times of various genes and their levels of expression in exponentially growing CHO cells were compared. Although there was a general correlation between transcriptional activity and replication in the first half of S phase, examination of specific genes revealed a number of exceptions. Approximately 25% of total poly(A) RNA was transcribed from the late-replicating DNA.

Ferritin H gene polymorphism in idiopathic hemochromatosis

The authors studied the H ferritin restriction polymorphism in 83 hemochromatosis patients and 84 controls as well as in 19 nuclear families. No significant difference was found with the ten restriction enzymes used (HindIII, EcoRI, EcoRV, PvuII, BamHI, PstI, Bg/I, Bg/II, HincII, and TaqI). Hence, the genomic abnormality responsible for idiopathic hemochromatosis is not a major deletion of an H ferritin gene. A higher frequency of one HindIII fragment, although nonsignificant when the number of comparisons made is taken into account, was observed in the patients. This HindIII fragment hybridizes with the H ferritin probe and with a 28 S ribosomal probe, and its segregation with HLA haplotypes (hence its assignment to chromosome 6) is uncertain. Its possible meaning in the expression of the disease is discussed.