Regulation of bcl-2 proto-oncogene expression during normal human lymphocyte proliferation

The bcl-2 and c-myc proto-oncogenes are brought into juxtaposition with the immunoglobulin heavy chain locus in particular B-cell lymphomas, resulting in high levels of constitutive accumulation of their messenger RNAs. Precisely how the products of the bcl-2 and c-myc genes contribute to tumorigenesis is unknown, but observations that c-myc expression is rapidly induced in nonneoplastic lymphocytes upon stimulation of proliferation raise the possibility that this proto-oncogene is involved in the control of normal cellular growth. In addition to c-myc, the bcl-2 proto-oncogene also was expressed in normal human B and T lymphocytes after stimulation with appropriate mitogens. Comparison of the regulation of the expression of these proto-oncogenes demonstrated marked differences and provided evidence that, in contrast to c-myc, levels of bcl-2 messenger RNA are regulated primarily through transcriptional mechanisms.

Elevated adenosine deaminase activity and hereditary hemolytic anemia. Evidence for abnormal translational control of protein synthesis

We have investigated the molecular basis of the marked elevation in erythrocyte adenosine deaminase (ADA) activity in a kindred with hereditary hemolytic anemia. Red cell ADA-specific activity was verified to be 70- to 100-fold normal levels. Western blots demonstrated a corresponding increase in erythrocyte ADA-specific immunoreactive protein. Analysis of genomic DNA revealed no evidence for amplification or major structural changes in the ADA gene. ADA-specific messenger RNA (mRNA) from proband reticulocytes was comparable in size and amount to mRNA from control reticulocytes. Translation of proband poly A+ reticulocyte mRNA in a rabbit reticulocyte lysate system and immunoprecipitation of 35S-labeled protein products with anti-ADA antibody yielded a band of approximately 42,000 apparent mol wt that was absent in translation products from control reticulocyte mRNAs. These data suggest that the increased ADA activity in red cells in this disorder results from the increased translation of an aberrant ADA mRNA.

Cloning of a rabbit erythroid-cell-specific lipoxygenase mRNA

We report the isolation of cDNA recombinants representing part of the rabbit reticulocyte (immature red blood cell, RBC) lipoxygenase (LOX) mRNA. One cDNA predicts an amino acid (aa) sequence matching exactly the unique N-terminal 30-aa sequence of the purified enzyme. Further, the reticulocyte mRNA, hybrid-selected by this recombinant, can be translated in vitro to give a polypeptide that comigrates with the purified reticulocyte LOX and is recognized by affinity-purified anti-RBC LOX polyclonal antibodies. Southern blotting experiments hybridising the RBC LOX cDNAs available to total rabbit genomic DNA digested with various restriction enzymes gives a fairly simple hybridisation pattern under moderate stringency conditions: moreover, the same pattern is obtained with a cloned fragment of genomic DNA containing the RBC LOX gene. This indicates that the RBC LOX gene is unique in the genome and seems not to be very closely related to the genes encoding the other tissue LOXs. We also show by Northern transfer/hybridisation experiments that the RBC LOX mRNA is expressed only in the red cell lineage but not in white blood cells (bone marrow or spleen) or in other non-erythroid cells tested (e.g., brain and lung).

Transcription unit of the chicken histone H5 gene and mapping of H5 pre-mRNA sequences

We have analyzed the transcription unit of the gene coding for the erythrocyte-specific histone H5. RNA transcripts elongated in vitro by permeabilized immature cells hybridized to the template strand of the structural gene as well as to 3'-flanking sequences. Approximately 90% of the engaged RNA polymerase II molecules terminate transcription within a region of about 500 base pairs immediately downstream of the polyadenylation site. S1 nuclease protection experiments indicated that the downstream sequences are also transcribed in vivo, their relative amounts reflecting the distribution of RNA polymerases observed in vitro. RNA molecules extending up to 1.14 kilobase pairs downstream of the polyadenylation site were detected, but no unique site of termination was found. The sequence of the transcription termination region shows no obvious homology to those of other RNA polymerase II termination regions. The possible involvement of altered DNA and/or chromatin structures in the transcription termination process is discussed.

HLA-DR-associated invariant chain is highly expressed in chronic lymphocytic leukemia

Total RNA extracted from peripheral blood lymphocytes of a patient with B-cell chronic lymphocytic leukemia (CLL) and the poly (A+) RNA was purified. A cDNA library was constructed and approximately 4,000 clones were screened in order to identify genes preferentially expressed in CLL. A relatively low repetition frequency characterizes the majority of the abundant mRNA species present in CLL lymphocytes. One clone, corresponding to the mRNA encoding the HLA-DR-associated invariant chain, was selected and its expression was examined in different leukemic cell populations and in normal tissues. DNA-RNA hybridization studies showed that the invariant chain mRNA (In-mRNA) is detectable in RNA preparations from human blood cells and their precursors, whereas no In-mRNA is found in several other tissues examined. Among various normal and leukemic leukocyte populations, the highest levels of In-mRNA are found in CLL. Therefore, a role of In-chain mRNA as a marker of CLL is proposed. Our data support a relationship between high levels of invariant chain mRNA and the out of cycle condition of CLL peripheral blood lymphocytes.

Control of protein synthesis by amino acid supply. The effect of asparagine deprivation on the translation of messenger RNA in reticulocyte lysates

The enzyme asparaginase, which hydrolyses asparagine to aspartic acid, inhibited cell-free protein synthesis by reticulocyte lysates. The inhibition was rapid and complete when sufficient enzyme was added but could be prevented or reversed by the addition of asparagine. The initial effect of asparaginase appears to be a block in polypeptide chain elongation due to asparagine deprivation, but there are some indications that prolonged incubation under these conditions may give rise to a secondary decrease in initiation of protein synthesis.

mRNA and apolipoprotein E synthesis abnormalities in peripheral blood monocyte macrophages in familial apolipoprotein E deficiency

We have studied synthesis of apolipoprotein E (apo-E) and apo-E mRNA in cultures of peripheral blood human monocyte macrophages (M-M cultures) obtained from a patient with familial apolipoprotein E deficiency. We have found that the M-M cultures of the apo-E-deficient patients contained two apo-E mRNA species with slightly different molecular weight as compared to normal apo-E mRNA. The apo-E mRNA concentration of the apo-E-deficient cultures was approximately 50-fold reduced as compared to the normal cultures, whereas the actin mRNA concentrations were identical in both M-M cultures. Genomic blotting analysis using a full-length apo-E cDNA clone as hybridization probe did not show gross differences between the restriction patterns of the DNA obtained from the apo-E-deficient patient and two normal controls. When normal M-M cultures were grown in media containing [35S]methionine they synthesized and secreted apo-E into the culture media. In contrast we could not detect any intracellular or extracellular apo-E in the patient's M-M cultures grown under identical conditions. These observations are consistent with the hypothesis that familial apo-E deficiency results from structural apo-E gene mutation(s). The putative mutation(s) affect either the transcription of the apo-E gene or the processing of the primary apo-E mRNA transcript. These abnormalities are associated with low levels of synthesis of aberrant apo-E mRNA forms which are either very unstable or cannot be translated into protein.

Compensatory increase in alpha 1-globin gene expression in individuals heterozygous for the alpha-thalassemia-2 deletion

alpha-Globin is encoded by the two adjacent genes, alpha 1 and alpha 2. Although it is clearly established that both alpha-globin genes are expressed, their relative contributions to alpha-globin messenger RNA (mRNA) and protein synthesis are not fully defined. Furthermore, changes that may occur in alpha-globin gene activity secondarily to the loss of function of one or more of these genes (alpha-thalassemia [Thal]) have not been directly investigated. This study further defines the expression of the two human alpha-globin genes by determining the relative levels of alpha 1 and alpha 2 mRNA in the reticulocytes of normal individuals and in individuals heterozygous for the common 3.7-kilobase deletion within the alpha-globin gene cluster that removes the alpha 2-globin gene (the rightward type alpha-Thal-2 deletion). To quantitate accurately the ratio of the two alpha-globin mRNAs, we have modified a previously reported S1 nuclease assay to include the use of 32P end-labeled probes isolated from alpha 1- and alpha 2-globin complementary DNA recombinant plasmids. In individuals with a normal alpha-globin genotype (as determined by Southern blot analysis [alpha alpha/alpha alpha]), alpha 2-globin mRNA is present at an average 2.8-fold excess to alpha 1. In individuals heterozygous for the rightward type alpha-Thal-2 deletion (-alpha/alpha alpha) the alpha 2/alpha 1 mRNA ratio is 1:1. These results suggest that the loss of the alpha 2-globin gene in the alpha-Thal-2 deletion is associated with a 1.8-fold compensatory increase alpha 1-globin gene expression.

In vitro synthesis of low molecular weight proteins in human platelets: absence of labelled release products

Isolated human blood platelets incubated at 37 degrees C in vitro incorporated labelled amino acids into compounds which included some low molecular weight (less than 80KDa) proteins, as determined by autoradiography after sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions. Non-dialysable plasma factor(s) inhibited both uptake and incorporation, which although unaffected by Actinomycin D, was inhibited partly by Chloramphenicol and almost completely by Puromycin and Cycloheximide, results which confirm that synthesis is directed by pre-existing mRNAs, some of which is mitochondrial. Assuming that the mRNA coding for proteins which are truly "platelet specific" must be present in megakaryocyte cytoplasm, we investigated the possibility that such RNA may be sufficiently stable for its translation to continue in platelets. Although leakage from platelet alpha-granules and cytoplasm during incubation was negligible and platelets retained their secretory potential we were unable to detect radiolabelled proteins in thrombin-released material after incubation. We conclude that either alpha-granule proteins are not synthesised in platelets or their megakaryocyte progenitors, or that their mRNAs become degraded by the time platelets reach the peripheral circulation. Alternatively, the mechanism which concentrates these proteins in granules does not function in circulating platelets.

The expression of human interferon alpha genes

We have determined the levels of mRNAs for IFN-beta, IFN-gamma and various alpha-IFNs (IFN-alpha 1, -alpha 2, -alpha 4, -alpha 5, -alpha 6, -alpha 7, -alpha 8 and -alpha 14) in normal and leukaemic human blood leucocytes and several cell lines induced in different fashions. The ratio of alpha to beta IFN transcripts varied greatly, depending on the cell type. The levels of the individual IFN-alpha RNAs were very different: IFN-alpha 1, -alpha 2 and -alpha 4 RNAs constituted the major fraction of the IFN-alpha transcripts measured, while IFN-alpha 6, -alpha 7, -alpha 8 and -alpha 14 were minor components in normal, induced leucocytes. Moreover, there was a striking difference in the proportion of individual IFN-alpha mRNA species in different cell types, in particular between normal and leukaemic cells; for example all cases of myeloblastic leukaemia examined showed a high expression of IFN-alpha 14. Use of different induction protocols did not significantly affect the proportion of IFN mRNAs. Analysis of the human IFN-alpha 1 gene by reversed genetics led to the identification of a segment of 5' flanking sequence between positions 117 and 68 upstream of the cap site which is required for inducibility by virus.

Rapid qualitative changes in mRNA populations in cultured human lymphocytes: comparison of the effects of cycloheximide and concanavalin A

To examine the hypothesis that the stimulation of cultured lymphocytes by lectins involves the inactivation of a protein repressor of putative "activation genes," the effects of a protein synthesis inhibitor (cycloheximide) and a lectin (concanavalin A) were compared. Qualitative changes in mRNA populations were assessed by translating RNA prepared from cycloheximide- or lectin-treated cultures in a rabbit reticulocyte lysate. [35S]Methionine-labelled translation products were analysed by two-dimensional polyacrylamide gel electrophoresis. Cycloheximide increased the radioactive labelling of cultured lymphocytes with the RNA precursor [3H]uridine, as previously reported. This was observed during the first 3 h of culture; thereafter, cycloheximide was inhibitory. The period of increased labelling with [3H]uridine coincided with a period of great increase in mRNA corresponding to an acidic protein of a relative mass of approximately 55 000. This mRNA was not detected in RNA prepared from control cultures, but was one of the most abundant mRNA species detected in RNA prepared from cycloheximide-treated cultures. Increases in certain less abundant mRNA species were also noted. However, the mRNAs were not observed in RNA prepared from lectin-treated cultures. If an increase in these mRNAs is important for lymphocyte activation, then the increase must be to an extent not detected by our current methods.

Developmental regulation of globin and nonglobin messenger RNAs in avian erythroid cells

During embryonic development in the chicken two morphologically distinct erythroid cell populations sequentially appear. Coincidentally with the change in cell populations that begins on the sixth day of embryonic life, the hemoglobins of the early embryo are gradually replaced by a new set of hemoglobins, which are almost identical to those of the adult chicken. We have used recombinant DNAs to investigate the molecular mechanisms underlying these developmental changes. With respect to the eight nonglobin species of messenger RNA that we have studied, seven are present at approximately equal concentrations in erythroid cells from 5-day embryos and from anemic adults. This suggests that the replacement of erythroid cell populations is not accompanied by a general reorganization of gene expression. With respect to globin gene expression, however, we find that all but one of the globin genes studied (alpha D-globin) undergo dramatic developmental regulation. We have also shown that the expression of the gene for the embryo specific alpha-like globin, pi'-globin, is principally regulated at the level of transcription.

Lineage-specific and differentiation-stage-specific gene expression in normal and leukaemic human myeloid cells

One example of each of two approaches to the isolation of molecular hybridization probes and their use for the comparative investigation of gene expression and its control during differentiation of normal and leukaemic leukocytes is described. RNA preparations from the peripheral blood leukocytes of human leukaemias of various types were assayed for the relative abundance of the mRNA homologous with a cellular oncogene, c-myc. All types of leukaemia except chronic lymphatic leukaemia (CLL) showed varying levels of myc-related RNA; the highest concentrations occurred in cell populations in which blast cells predominated. In contrast, a recombinant plasmid (pCG14), isolated from a cDNA recombinant plasmid library that represented polyadenylated RNAs from the peripheral blood leukocytes of a chronic granulocytic leukaemia (CGL), hybridized with an mRNA whose occurrence is diagnostic of CGL leukocytes. This mRNA was also found in normal bone marrow cells; in both bone marrow and in CGL leukocytes, pCG14-homologous RNA occurs only in cells around the myelocyte stage in differentiation. It is suggested that these probes, and others for mRNAs whose occurrence is specific to a particular cell lineage and/or stage in differentiation, detect a new series of potential diagnostic markers. These might usefully supplement existing ones to provide a more detailed, objective subclassification of the leukaemias which could have important implications for diagnosis and therapy.

Beta globin messenger RNA content of bone marrow erythroblasts in heterozygous beta-thalassemia

RNA from bone marrow erythroblasts and peripheral blood reticulocytes of patients with heterozygous beta-thalassemia was analyzed for relative content of alpha and beta globin messenger RNA by molecular hybrization. Erythroblasts from nonthalassemic patients exhibited approximately the same alpha and beta globin mRNA content (beta/alpha mRNA ratio = 0.8-1.0) as circulating reticulocytes (beta/alpha mRNA ratio = 0.74-1.2). The mRNA ratios corresponded well to levels of globin synthesis observed in bone marrow and peripheral blood. Erythroblasts from four patients with heterozygous beta-thalassemia also exhibited approximately the same beta/alpha mRNA ratios in bone marrow erythroblasts (0.34-0.59) as in reticulocytes (0.34-0.4): beta globin mRNA was clearly deficient in bone marrow erythroblasts. Globin biosynthesis by erythroblasts of beta-thalassemia heterozygotes was balanced despite the mRNA deficiency (beta/alpha = 0.9-1.0), suggesting that post-translational phenoma (eg, proteolysis of free globin chains), rather than instability of beta mRNA, accounts for the balanced globin chain synthesis frequently observed in bone marrow erythroblasts of patients with beta-thalassemia trait.

Plasma human chorionic somatomammotropin deficiency in a normal pregnancy is the consequence of low concentration of messenger RNA coding for human chorionic somatomammotropin

Human chorionic somatomammotropin (hCS) is important in the hormonal monitoring of human pregnancies. Presented is the case of a clinically normal pregnancy in which a very low plasma level of hCS was detected. The concentration of messenger ribonucleic acid (mRNA) coding for hCS was evaluated to determine the level on which the deficiency occurred.

The translation of the messenger for the poly(A)-binding protein-associated with translated mRNA is suppressed. A case of cytoplasmic repression in duck erythroblasts

In vivo protein synthesis in duck erythroblasts was compared to in vitro translation of polyribosomal and free cytoplasmic mRNA. The in vivo study showed the absence of de novo synthesis of the Mr 73 000 poly(A)-binding protein found associated with all polyribosomal mRNA. In vitro translation demonstrated that the mRNA for this protein is absent from the polyribosomal mRNA fraction but constitutes a medium frequency messenger among the repressed free mRNA. This result confirms the existence of a qualitative translational control in terminal differentiating duck erythroblasts leading eventually to the arrest of the protein synthesizing machinery.

Haemoglobin Constant Spring has an unstable alpha chain messenger RNA

Haemoglobin Constant Spring (Hb CS) is a variant with an elongated alpha-chain associated with an alpha + thalassaemia phenotype. The amount of alpha mRNA relative to beta mRNA in reticulocytes was reduced in carriers of Hb CS by an amount equivalent to the reduction observed in carriers of alpha + thalassaemia. In a patient with Hb CS-H disease there was greater alpha/beta mRNA ratio in bone marrow nuclear RNA than in the peripheral blood. Furthermore, all the alpha mRNA in the patient's peripheral blood was derived from the alpha 1 (alpha A) gene. The data suggest that alpha CS mRNA is unstable and degraded in the cytoplasm. This instability may be due to destabilization of a specific sequence in the 3' non-coding region during translation.

Differing responses of globin and glycophorin gene expression to hemin in the human leukemia cell line K562

The human leukemia cell line, K562, produces embryonic and fetal hemoglobins and glycophorin A, proteins normally associated only with erythroid cells. Hemoglobin accumulation is enhanced by exposure of the cells to 0.05 mM hemin. We have examined K562 cells before and after exposure to hemin to determine whether expression of these erythroid proteins was shared by all cells or confined to specific subpopulations. Globin gene expression was examined by quantitation of globin mRNA sequences, using a 3H-globin cDNA molecular hybridization probe. Constitutive cells produced globin mRNA, the content of which was increased 3-4-fold by hemin. Cell-to-cell distribution of globin mRNA was determined by in situ hybridization of 3H-globin cDNA to constitutive and hemin-treated K562 cells. Virtually all cells in the culture exhibited grain counts above background, indicating globin gene expression by all cells, rather than a confined subpopulation. Virtually all hemin-treated cells had 3-5-fold higher grain counts, indicating uniformly increased globin gene expression. The glycophorin content of K562 cells was estimated by fluorescence-activated cell sorting (FACS) of cells labeled with fluorescein-labeled antiglycophorin antiserum. The vast majority of constitutive cells contained glycophorin, but exhibited to apparent increase in glycophorin accumulation after hemin exposure. Thus, glycophorin and globin genes exhibited differential responses to hemin. These differences could reflect normal differences in the patterns of specialized gene expression in stem cells. Alternatively, different aberrations of gene expression could be occurring in response to the determinants of the neoplastic properties of K562.

Stability of polyadenylated mRNA in pig lymphocytes

The stability of cytoplasmic poly(A)-containing mRNA in unstimulated pig lymphocytes has been determined by [3H]poly(U) hybridization after actinomycin D treatment. This approach has shown that the majority of the mRNA is much more unstable than has been suggested by earlier pulse-chase experiments, and has a half-life of between 1 and 2 h.

Identification and characterization of the translationally repressed cytoplasmic globin messenger-ribonucleoprotein particles from duck erythroblasts

Globin messenger ribonucleoprotein (mRNP) particles which have been isolated from duck erythroblast post-polyribosomal supernatant are translationally inactive in vivo and in vitro but contain translatable mRNA active after deproteinisation. They were characterized following purification by successive sucrose gradient sedimentation in a buffer containing 0.05 M KCl. The complex, which sediments homogeneously at about 20 S, has a density of 1.39 g/cm3 and thus consists of four parts protein to one part RNA; 40% of this RNA is globin mRNA and no other mRNA could be detected. Sedimentation of the purified globin mRNP on sucrose gradients in 0.5 M KCl produced four components while polyacrylamide gel electrophoresis in non-denaturing conditions and in the presence of EDTA resulted in the separation of three components. Hybridization to globin cDNA and translation in vitro of the RNA extracted from these subparticles revealed the existence of two core particles containing globin mRNA with nominal sedimentation coefficients of 13 S and 16 S. Analysis of the protein components of the isolated sub-complexes by dodecyl sulfate and bidimensional gel electrophoresis indicated a very characteristic protein composition for each of these complexes. The 16-S and 13-S globin mRNPs differed essentially by the presence in the 13-S mRNP only of a group of major polypeptides. Of the other two sub-complexes, one consisted of 90% small RNA in the 4-S range; the second sedimented ahead of the globin mRNP core particles at about 19S and consisted of a very characteristic set of about 14 polypeptides. The polyribosomal 73000-Mr poly(A)-binding protein was not detected in the purified free globin mRNP although the mRNA in the untranslatable particle is polyadenylated. The presence in the cytoplasm of duck erythroblasts of two forms of untranslated globin messenger ribonucleoprotein particles, distinct in their protein composition from polyribosomal globin mRNP, suggests that they may have a specific role in the regulation of translation of globin mRNA.

The genetic basis of Hb Q-H disease

A Chinese family has been studied in which two siblings have haemoglobin Q-H disease. Using a combination of haematological and haemoglobin analysis, globin chain synthesis, analysis of alpha/beta globin messenger RNA ratios and restriction endonuclease mapping, it has been shown that each of these siblings has received one chromosome on which both alpha chain genes have been deleted and another on which there is only a single alpha chain locus which carries the alpha Q mutation. Their genotype is thus --/-alpha Q. Despite the fact that the haemoglobin Q mutation in this family is carried on a chromosome with a single alpha chain locus, heterozygous carriers for the variant have only 25% or less haemoglobin Q. Our observations indicate that the molecular basis for haemoglobin Q-alpha thalassaemia is similar to that for the common form of haemoglobin H disease in Orientals. Furthermore, they provide clear evidence that the level of an alpha chain variant in heterozygous carriers is not a reliable reflection of the number of alpha globin genes.

Unequal alpha and beta globin mRNA in reticulocytes of normal and mutant f/f fetal mice

Messenger RNA (mRNA) was isolated from adult as well as normal and mutant f/f fetal mouse reticulocytes by poly-U affinity chromatography. mRNA from normal adult reticulocytes directed equal synthesis of alpha and beta globin chains in wheat germ cell free translational system. mRNA from either normal or mutant f/f fetal reticulocytes directed 40% more alpha globin synthesis than beta globin synthesis. These observations are suggestive that there is significantly more alpha mRNA than beta mRNA in normal and mutant f/f fetal mouse reticulocytes.

Translational activity of messenger ribonucleic acid isolated from unstimulated and phytohaemagglutinin-activated lymphocytes

Purified cytoplasmic poly(A)+ RNA isolated from unstimulated pig lymphocytes has the same ability to direct translation in a range of cell-free systems as the corresponding mRNA from 20h phytohaemagglutinin-activated lymphocytes. Additional methylation of the mRNA is not required for maximum protein synthesis in the wheat-germ cell-free system. Misleading results are obtained if the mRNA preparations used are not adequately purified, and a method suitable for routine assessment of the degree of purification achieved is described. Cell-free protein-synthesizing systems from unstimulated lymphocytes translate added lymphocyte mRNA with lower efficiency than do comparable systems from phytohaemagglutinin-activated lymphocytes, whatever the source of the mRNA used.

Inhibition by dexamethasone of commitment to erythroid differentiation in murine erythroleukemia cells

The inhibition of erythroid differentiation of murine erythroleukemia cells by dexamethasone (DEX) has been investigated on a clonal basis. At concentrations which had no detectable effect on cell proliferation, DEX3 rapidly inhibited the dimethyl sulfoxide (DMSO)-induced commitment of individual murine erythroleukemia cells to the differentiation program. DEX did not prevent heme accumulation in cells already committed to the differentiation process. The rate of globin messenger RNA (mRNA) synthesis was reduced in cells treated with DMSO and DEX compared to cells treated with DMSO alone. The reduction in the rate of globin mRNA synthesis was proportional to the reduction caused by DEX in the rate of commitment. DEX inhibition in the rate of commitment and of globin mRNA synthesis of DMSO-treated cells was reversible. Upon removal of DEX, continued DMSO treatment resulted in a rapid increase in both the rate of globin mRNA synthesis and the rate of commitment. The rate of globin mRNA synthesis after DEX release was also proportional to the rate of commitment. These results suggest that DEX exerts an inhibitory effect on heme and globin synthesis by blocking commitment to terminal erythroid differentiation.

The identification of globin messenger ribonucleic acid in newt erythropoietic cells

Polyadenylated [poly(A)+]-RNA isolated from newt (Triturus cristatus) erythropoietic cells contained two main species sedimenting at 9S and 25S, and minor amounts of a 15-20S component. The 9S poly(A)+-RNA fraction induced synthesis of newt haemoglobin and globins in frog oocytes and in an mRNA-dependent rabbit reticulocyte lysate, confirming its identity as newt globin mRNA. Translation of 9S globin mRNA in reticulocyte lysate was concentration-dependent, the patterns of globin synthesis suggesting both preferential utilization and unequal amounts of the different globin mRNA subspecies. Globin mRNA activity was also evident in the 25S poly(A)+-RNA fraction whose localization in polyribosomes excluded its function as a nuclear globin mRNA precursor. Denaturation in formamide and estimation of its relative methyl content indicated that the 25S poly(A)+-RNA fraction contained equimolar amounts of 9S globin mRNA and 26S rRNA. Translation of the 25S fraction in reticulocyte lysate was less efficient than that of comparable amounts of 9S globin mRNA and induced a pattern of globin synthesis similar to that obtained with subsaturating amounts of 9S mRNA. The 25S mRNA-rRNA complex was considered to be a non-physiological aggregate generated by extraction of RNA in the presence of buffers of moderate to high ionic strength.

Quantitation and localization of globin messenger RNA in rabbit reticulocyte lysate

A sensitive and quantitative method is described for the determination of globin mRNA distribution in rabbit reticulocyte lysate. The method uses high resolution sucrose density gradient centrifugation followed by [5'-3H]polyuridylate hybridization to poly(A)-mRNA in gradient fractions. Polyadenylate, purified globin mRNA, and ribonuclease-treated lysate are used to standardize the hybridization assay. It is demonstrated that changes of mRNA and ribosomal distribution do not affect quantitation of the total mRNA localization and Met-tRNAf which suggest that the monitoring of Met-tRNAf binding alone may not be sufficient to assess the mechanisms of control which affect the initiation of protein synthesis.

In vivo degradation of rat globin messenger RNA during maturation of reticulocytes

The degradation of globin mRNA in rat reticulocytes maturing in the peripheral blood was investigated. Poly(A) and non poly(A) portions of mRNA molecules were determined quantitatively by hybridization with radioactive poly(U) and complementary DNA, respectively. During the degradation of mRNA in vivo, it was shown that (1) globin mRNA and the bulk of RNA decrease in parallel, (2) the average chain length of poly(A) segments in the mRNA does not change, (3) the percentage of poly(A) (-) globin mRNA in total globin mRNA does not change, and (4) fragments of large molecular weight do not accumulate. Possible mechanisms of degradation of globin mRNA in the reticulocytes are discussed on the basis of these observations.

beta 0 thalassemia, a nonsense mutation in man

We determined the complete nucleotide sequence of the 5' noncoding region and the first 74 amino acids of the nonfunctional beta-globin mRNA in a patient with homozygous beta 0 thalassemia. We identified the molecular defect as a single nucleotide substitution in the coding region of the mRNA. At the position corresponding to amino acid 17, replacement of an adenine by a uracil changes the triplet AAG, which codes for lysine in the normal beta chain, to an amber termination codon, UAG. This type of beta 0 thalassemia represents an example of a nonsense mutation in man.

Free cytoplasmic messenger ribonucleoprotein complexes from rabbit reticulocytes

Free cytoplasmic globin mRNA containing mRNP-particles were isolated from rabbit reticulocytes by zonal sucrose gradient centrifugation and their properties were compared with mRNP particles isolated in the same way from EDTA-dissociated reticulocyte polyribosomes. The average poly(A)-length of 9S mRNA from free cytoplasmic mRNP was 17-20 nucleotides being about two times shorter than the average poly(A)-length of polysomal 9S mRNA. The protein composition of the free cytoplasmic mRNP particles disclosed the absence of the 76,000 dalton protein which is associated with the 3'poly(A)-segment of polysomal globin mRNA. It was concluded that free cytoplasmic mRNP-particles from rabbit reticulocytes can be classified as "old" mRNP in a post-translational phase. Free cytoplasmic mRNPs were translated in heterologous cell-free systems as well as in Xenopus laevis oocytes. Addition of hemin stimulated the synthesis of alpha-globin in all systems, while the presence of the cap analogue m7G(5')p inhibited translation of free cytoplasmic mRNA completely. The latter finding suggested that free cytoplasmic mRNA has a 5' terminal "cap". Shortening of the poly(A)-segment with concomitant loss of the 76,000 dalton protein may lead to less efficient translation of free cytoplasmic mRNP.

Globin messenger precursor RNA in duck immature red blood cells

A procedure is described for the chromatographic analysis of RNA under fully denaturing conditions on cross-linked Sepharose. Chromatography of DNA . RNA hybrids, poly(C) . poly(G) hybrids and complexes of poly(C) . hnRNA on Sepharose CL in pure formamide at 46 degrees C leads to denaturation and strand separation of the hybrid structures. Using this procedure, nuclear RNA from duck immature red blood cells was resolved according to molecular size and assayed for the presence of globin mRNA sequences by hybridization with complementary DNA. Two size classes of putative globin mRNA precursor molecules were detected at an elution position corresponding to 14--18 S and 23--28 S. As judged from chromatographic analysis on poly(U)-Sepharose, about 70% of the 14--18-S globin precursor RNA is polyadenylated while only 11% of the putative 23--28-S precursor RNA has a poly(A) tract. Inhibition of transcription by actinomycin D and pulse-chase experiments indicate a half-life of less than 7.5 min for these precursor RNA species.

Globin-chain synthesis in Hb H disease: the activity of red cell precursors and their mRNA

Globin-chain synthesis was determined in bone marrow and blood of four patients with Hb H disease and in a cell-free system supplemented with poly(A)-rich RNA from the patients. The relative synthesis of alpha-globin ranged between 0.36 and 0.49 in erythroid precursors and between 0.09 and 0.28 in reticulocytes. The relative quantity of biologically active alpha-globin mRNA in poly(A)-rich RNA from bone marrow and blood of these patients ranged between 0.09 and 0.21. The findings suggest the operation, within alpha-thalassemic bone marrow cells, of a translational control mechanism and/or the instability of alpha-globin mRNA.

Absence of beta mRNA in beta0-thalassemia in Kurdish Jews

We report the characterization of the amount of beta mRNA in a Kurdish Jewish population with beta0-thalassemia using the same methods employed for characterization of the Catania and Ferrara beta0 patients. We found very low amounts of beta mRNA sequences, consistent with the presence of beta0-thalassemia of the beta mRNA-negative population type. In addition, no globin gene deletion was detected that could account for the absence of beta mRNA.

Isolation and characterization of the messenger RNAs for mouse embryonic globin chains

Messenger RNAs for mouse embryonic globins were purified from yolk sac erythroid cells by oligodeoxythymidilate-cellulose chromatography and sucrose density centrifugation. Full-sized complementary DNA copies of embryonic globin mRNAs were synthesized. Acrylamide gel electrophoresis of these RNAs indicate an average molecular weight of 220 000, including a polyadenylated sequence of about 35 residues, as determined by hybridization to [3H]polyuridylate. The wheat-germ translation products of mRNAs have the size and the ionic characteristics of the four embryonic globin chains alpha, x, y and z. Hybridization kinetics in vast RNA excess were performed and compared to standard r0t curves of adult globin messengers, demonstrating a total base sequence complexity of about 880 000 daltons, that is four different RNA sequences of 220 000 molecular weight. The titration of embryonic globin cDNAs with increasing amounts of their complementary RNA templates indicates that the embryonic globin messengers were isolated at a high degree of purity.

Variability in the amount of beta-globin mRNA in beta0 thalassemia

Globin mRNA isolated from a number of beta0 thalassemia patients of different ethnic origins was analyzed by RNA-cDNA hybridization and, in two cases, by fingerprint analysis of 125I-labeled mRNA. Quantitation of the relative amounts of alpha- and beta-mRNA by hybridization to purified alpha-and beta-cDNA revealed that in approximately half the cases, there was less than 1% as much beta-mRNA as alpha-mRNA. In the rest of the cases, low levels of beta-like mRNA were detected in amounts 4-12% as abundant as alpha-mRNA. There was variability in the yield of beta-like mRNA in patients of the same racial group, in the same patient at different times and in similarly affected siblings: beta-mRNA was virtually absent in some samples, whereas low but significant levels were found in other samples. In one patient, beta-like mRNA was not detected in peripheral blood RNA, but was present in the RNA of bone marrow cells. In one case, the thermal stability of the beta0 thalassemia mRNA-beta-cDNA hybrid was measured and found to be slightly lower than that of the authentic beta-mRNA-beta-cDNA hybrid. In none of the cases tested was there synthesis of beta-globin chains directed by beta0 thalassemia mRNA in a cell-free protein-synthesizing system, even when beta-like mRNA was detected in the sample by hybridization assays. mRNA from two patients was labeled in vitro with 125I, digested with T1 RNAase and fractionated in two dimensions. Analysis of the resulting fingerprints revealed the presence of prominent alpha chain-specific oligonucleotides without detectable beta chain-specific oligonucleotides, and thereby confirmed the results of hybridization assays showing absent or very low levels of beta-mRNA in the same RNA samples. Our results support the concept that beta0 thalassemia is heterogeneous in its molecular basis even within the same racial group: in some patients, it is associated with absent beta globin mRNA, whereas in other patients, it is associated with low but significant levels of nonfunctional beta or beta-like globin mRNA. The variable amounts of beta-like mRNA detected in different samples from the same patient, and in patients with the same genotype, indicate that as yet undefined factors can influence the yield of beta-like mRNA observed in beta0 thalassemia.

Characterization of beta-globin mRNA in the beta0 thalassemias

A number of cases of beta0 thalassemia have been examined for the presence or absence of beta-globin mRNA. Total RNA extracted from peripheral blood was hybridized to purified complementary DNA specific for beta-globin mRNA, and to beta-cDNA probes specific for the 5' and 3' noncoding regions of beta-globin mRNA. Three clear-cut categories of beta0 thalassemia were identified. The first type had no detectable beta-globin mRNA. A second typed had beta-globin mRNA sequences which hybridized incompletely to the cDNA probes and probably represented mRNAs with grossly altered structures. A third type appeared to have essentially intact, though untranslatable, beta-globin mRNA. Depurination products from 5' and 3' beta-cDNAs synthesized from this latter mRNA were identical to those from normal beta-globin mRNA, but the relative yields were different, suggesting a possible defect near the initiation codon.

Isolation and characterization of free cytoplasmic messenger ribonucleoproteins from rabbit reticulocyte

Free cytoplasmic messenger ribonucleoproteins have been prepared with a high yield in a zonal rotor. They are rapidly labelled by [3H]uridine. Their sedimentation coefficients are 14.6 S and 19.4 S. Their protein contents are higher than in ribosomes, as indicated by a shift towards greater wavelength in their ultraviolet spectra and a buoyant density of 1.39 g cm-2 in CsCl. They do not cross-react with antiribosome antibodies and their protein patterns in sodium dodecylsulfate and two-dimensional polyacrylamide gel electrophoresis are different from ribosomes'. They may contain up to 30 proteins. The proteins are acidic and their molecular weights range from 22 000 to 100 000. When compared to chromatin they behave more like non-histone proteins than histones.

Translation of endogenous message in embryonic chick erythroid cell polysomes in a cell-free protein-synthesizing system

Polysomes from 5.5-day and 6.5-day embryonic chick erythroid cells contain messenger RNA (mRNA) which can be translated into products in a cell-free protein-synthesizing system. The products of the cell-free system coelectrophoresed with carrier globin chains from the cells from which the polysomal pellet was isolated. Wheat germ S30 fraction increases by 1.5--2.0 fold [3H] leucine incorporation into trichloroacetic acid-precipitable material directed by the endogenous mRNA on chick erythroid cell polysomes. The wheat germ probably provides a specific factor or factors absent in a shortage in the incubation medium.