The duck-globin messenger-ribonucleoprotein complex. Resistance to high ionic strength, particle gel electrophoresis, composition and visualisation by dark-field electron microscopy

Y-box Binding Protein 1: Looking Back to the Future

Y-box binding protein 1 is a member of the cold shock domain (CSD) protein family and one of the most studied proteins associated with a large number of human diseases. This review aims to critically reassess the growing number of pathological functions ascribed to YB-1 in the past decades. The focus is given on the important role of YB-1 and related CSD proteins in the physiology of normal cells. The functional significance of these proteins is highlighted by their high evolutionary conservation from bacteria to men, where they are ubiquitously expressed and involved in coordinating all steps of mRNA biogenesis, including transcription, translation, storage, and degradation. Their activities are especially important under conditions requiring rapid change in the gene expression programs, such as early embryonic development, differentiation, stress, and adaptation to new environments. Therefore, to define a precise role of YB-1 in tumorigenic transformation and in other pathological conditions, it is important to understand its basic properties and functions in normal cells, and how they are interrupted in complex diseases including cancer.

Y-box-binding protein 1 (YB-1) and its functions

This review describes the structure and functions of Y-box binding protein 1 (YB-1) and its homologs. Interactions of YB-1 with DNA, mRNAs, and proteins are considered. Data on the participation of YB-1 in DNA reparation and transcription, mRNA splicing and translation are systematized. Results on interactions of YB-1 with cytoskeleton components and its possible role in mRNA localization are discussed. Data on intracellular distribution of YB-1, its redistribution between the nucleus and the cytoplasm, and its secretion and extracellular functions are summarized. The effect of YB-1 on cell differentiation, its involvement in extra- and intracellular signaling pathways, and its role in early embryogenesis are described. The mechanisms of regulation of YB-1 expression in the cell are presented. Special attention is paid to the involvement of YB-1 in oncogenic cell transformation, multiple drug resistance, and dissemination of tumors. Both the oncogenic and antioncogenic activities of YB-1 are reviewed. The potential use of YB-1 in diagnostics and therapy as an early cancer marker and a molecular target is discussed.

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.

The protein responsible for the repeating structure of cytoplasmic poly(A)-ribonucleoprotein

A 75,000-dalton protein has been purified approximately 1,000-fold from rat liver, based on its capacity to organize poly(A) in a 27-residue repeating structure. This protein may be identified with the major polypeptide component of cytoplasmic poly(A)-ribonucleoprotein (RNP) previously described. The poly(A)-organizing activity of the protein is detected only in cytoplasmic fractions. Upon nuclease digestion of the 75,000-dalton protein-poly(A) complex, monomers, and higher multimers of RNP subunits can be resolved in a sucrose gradient. The sedimentation rate of the monomer is compatible with a composition of one 75,000-dalton protein molecule and one 27-residue segment of poly(A).

An assessment of the evidence for the role of ribonucleoprotein particles in the maturation of eukaryote mRNA

This article has sought to draw together, on the one hand, what is known of mRNA processing and its control and, on the other hand, what is known of the structure and validity of hnRNP and snRNP particles. At the same time, it has attempted to synthesize these two themes into a critical assessment of the evidence which suggests that the particles are intimately involved in processing. It cannot be said that the case is proven. The evidence is compelling but circumstantial. The last few years have seen the development of the first in vitro splicing systems (Weingartner and Keller, 1981; Goldenberg and Raskus, 1981; Kole and Weissman, 1982), the isolation of monoclonal antibodies to defined snRNP (Lerner et al., 1981a; Billings et al., 1982) and hnRNP proteins (Hugle et al., 1982), and the ability to use artificial lipid vesicles to transfer antisera (Lenk et al., 1982) and radioactive snRNA (Gross and Cetron, 1982) into cells. It is to be hoped that further refinements of these and other techniques will allow us to solve this, one of the major outstanding problems of molecular biology.

Possible involvement of messenger RNA-associated proteins in protein synthesis

Two distinct forms of globin messenger RNA were isolated from mouse spleen cells infected with Friend erythroleukemia virus: polyribosomal messenger ribonucleoprotein particles (15S mRNP), and their corresponding protein-free mRNAs obtained by chemical deproteinization. The translation efficiencies of both messenger forms were assayed in a Krebs II ascites cell-free system. Selective removal of RNA-binding proteins from the ascites cell lysate did not affect globin synthesis when the mRNA was supplied as 15S mRNP; deproteinized mRNA however was not translated. Only in the presence of two fractions of RNA-binding proteins was the protein-free mRNA translated. Some of the RNA-binding proteins have the same molecular weights and isoelectric points as the principal proteins of 15S mRNP.

Identification of casein kinase II and phosphorylated proteins associated with messenger ribonucleoproteins particles from reticulocytes

Messenger ribonucleoprotein (mRNP) particles, isolated from reticulocyte polysomes and purified by buoyant density centrifugation in metrizamide, contained an endogenous protein kinase activity. The cyclic-nucleotide-independent protein kinase phosphorylated casein using either ATP or GTP as the phosphoryl donor and had properties similar to casein kinase II, an enzyme previously purified and characterized from the post-ribosomal supernate of reticulocytes. Antibody prepared to casein kinase II was shown to inhibit the protein kinase activity in the mRNP particles. The endogenous enzyme phosphorylated four peptides (Mr 125 000, 107 000, 76 000 and 63 000) in the mRNP particle. Three of the four peptides, plus another (Mr 175 000), were phosphorylated by purified casein kinase II while two peptides (Mr 95 000 and Mr 76 000) were phosphorylated with casein kinase I. The mRNP particles were not substrates for the cAMP-dependent protein kinases.

Purification of messenger ribonucleoprotein particles from rabbit reticulocytes by zonal centrifugation in metrizamide

A large-scale purification procedure for messenger ribonucleoprotein (mRNP) particles from rabbit reticulocyte polysomes is described. The mRNP particles were dissociated from polysomes by treatment with urea and separated by differential centrifugation under conditions of high ionic strength. Zonal centrifugation in a metrizamide buoyant density gradient was the final purification step. One major class of mRNA particle was observed. The RNA was defined as mRNA by polyacrylamide gel electrophoresis and by globin production in a cell-free protein-synthesizing system. The twenty-three different proteins associated with the particle were a discrete set of proteins, which ranged in molecular weight from 175,000 to 23,500. The relative amount of each peptide in the particle was determined from a gel scan of the stained protein by computer simulation. None of the polypeptides comigrated with proteins from the 40-S and 60-S ribosomal subunits when analyzed by two-dimensional polyacrylamide gel electrophoresis.

Comparisons of proteins associated with duck-globin mRNA and its polyadenylated segment in polyribosomal and repressed free messenger ribonucleoprotein complexes

EDTA dissociation of polyribosomes from duck erythroblasts allowed us to isolate the 15-S globin messenger ribonucleoproteins (mRNP) by sucrose gradient centrifugation or affinity chromatography on poly(U)-Sepharose or oligo(dT)-cellulose columns. Their protein composition was compared by one and two-dimensional electrophoresis in sodium dodecyl sulfate to the free 20-S mRNP containing the repressed fraction of globin mRNA [Vincent, A., Civelli, O., Maundrell, K., and Scherrer, K. (1980) Eur. J. Biochem. 112, 617--633]. The protein composition of the 15-S mRNP isolated by these methods in different ionic strength conditions, was characterized by a major 73 000-Mr polypeptide and seven minor polypeptides with Mr ranging from 45 000 to 68 000, all of which are slightly basic, and about five acidic ones in the 80 000--130 000-Mr range. All these are retained in the 15-S mRNP core particle isolated at 0.5 M KCl. At low ionic strength, in addition, a specific group of acidic polypeptides in the Mr range 35 000--105 000 was also found associated with globin mRNA. Oligo(dT)-cellulose chromatography of mRNP digested with ribonucleases A and T1 indicated that the 73 000-Mr major protein is bound to the poly(A) segment; some other proteins resolved as minor components interact with both the poly(A) and non-poly(A) regions of globin mRNA. Characterization of proteins interacting with the poly(A) segment of non-polyribosomal globin mRNA in 20-S free mRNP demonstrated the absence of the polyribosomal 73 000-Mr poly(A)-binding protein. Furthermore, it confirmed that the protein compositions of translatable polyribosomal and repressed free globin mRNP are very different. Indeed, the respective core (0.5 M KCl) particles contain only two possibly common polypeptides. The specificity of proteins associated with globin mRNA in two different functional states shown here supports the hypothesis of a role of mRNP proteins in translational control of mRNA.

Identification in Xenopus laevis of a class of oocyte-specific proteins bound to messenger RNA

Proteins associated with poly(A)-rich RNA in Xenopus laevis oocytes have been identified in immature ovary homogenates using sucrose gradient centrifugation, oligo(dT)-cellulose fractionation and analysis by sodium dodecyl sulphate/polyacrylamide gel electrophoresis and two-dimensional acid/urea/sodium dodecyl sulphate gel electrophoresis. At least eight proteins are associated with ribonucleoprotein complexes and have the following properties. 1. Four major proteins, mRNP1-4, cosediment with poly(A)-rich RNA at 40--200 S, bind to oligo(dT)-cellulose and are oocyte-specific. These are very basic proteins with molecular weights of about 50 X 10(3), 52 X 10(3), 56 X 10(3), 59 X 10(3). 2. Two further proteins, mRNP5,6, molecular weights 75 X 10(3) and about 100 X 10(3), also co-isolate with poly(A)-rich RNA mRNP7 (Mr 16 X 10(3)) cosediments with poly(A)-rich RNA but fails to bind to oligo(dT)-cellulose. mRNP8 (Mr 22 X 10(3)) binds to oligo(dT)-cellulose but sediments more slowly than the bulk of poly(A)-rich ribunucleoprotein, at 30--70 S. 3. mRNP1-4 are present in immature oocytes but only mRNP3-4 are found in full-grown oocytes, while none of them could be detected in Xenopus liver or reticulocytes. These proteins are largely cytoplasmic, associated with free mRNP particles, and differ in molecular weight from proteins isolated from polysomal mRNPs in somatic tissues. 4. mRNP1-4 are very abundant in immature oocytes; sedimentation properties are consistent with a protein:RNA ratio of 4:1 (w/w). The sedimentation constant of mRNP particles is resistant to concentrations of ribonuclease A which degrade ribosomes, although mRNA isolated from these ribonuclease-treated particles appears to be partially degraded. The role of ribonucleoprotein complexes in the stability and storage of mRNA during oogenesis is discussed.

Heat shock induced alterations in polyadenylate metabolism in Drosophila melanogaster

We have studied the effect of heat shock on poly(adenylic acid) [poly(A)] metabolism in Drosophila melanogaster cells by using hybridization of ribonucleic acid (RNA) samples to [3H]poly(uridylic acid). Shortly after heat shock begins, cytoplasmic poly(A) decays rapidly. Two components were detected. Component I constitutes 46% of the total cytoplasmic poly(A) and decays with a half-life of 10 min. Component II (54% of total) is more stable. A half-life was not estimated for component II because new synthesis was not blocked. Studies on the size of cytoplasmic poly(A) indicate component I is completely degraded while component II remains essentially unchanged. Nuclear poly(A) increases rapidly, peaking at 2 or 3 times the normal level after 90 min of heat shock. Studies on the size of nuclear poly(A) indicate the increase is not due to addition of poly(A) to existing poly(A) segments nor appreciably to newly synthesized RNA unless transit time is markedly increased. We conclude that nuclear poly(A) is added in large part to already existing nonadenylated primers. Studies with RNA and protein synthesis inhibitors show RNA and protein synthesis are not required for the changes in poly(A). As the temperature is raised above 34--35 degrees C, the effect on poly(A) metabolism becomes more severe. Changes in external pH, without increased temperature, also alter poly(A) levels. Poly(A) changes may therefore be a rapid response to a variety of physiological factors.

Endogenous substrate for cyclic AMP-dependent protein kinase in adrenocortical polyadenylated messenger ribonucleoproteins

An endogenous polysomal cyclic AMP-dependent protein kinase specifically phosphorylates a 150,000-dalton peptide bound to an adrenocortical polyadenylated messenger ribonucleoprotein complex. There is a possibility that this protein is a physiological substrate of cyclic AMP-dependent protein kinase and that the phosphorylation and dephosphorylation of this substrate may be important in the translation control of adrenal polyadenylated messenger RNA.

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.

Ribonucleotide sequences non-adjacent to poly(A) participate in the poly(A)-protein complex in 15S duck globin mRNP particles

The study of the interaction between mRNA and proteins in the polyribosomal 15 S duck globin messenger ribonucleoprotein complex showed that proteins protect specific mRNA sequences against digestion by the nonspecific micrococcal nuclease (Nucleic Acids Research 6 (8) 2787, 1979). Here we report the isolation of the poly(A)-protein RNP complex from nuclease digested 15 S mRNP by two different methods: sucrose gradient sedimentation and oligo(dT)-cellulose chromatography. We show by fingerprint analysis, that aprt from the periodically fragmented poly(A) segment, mRNA sequences adjacent and non-adjacent to the poly(A) segment are protected by the poly(A) binding proteins against nuclease digestion. The duck globin poly(A)-protein RNP complex, with a sedimentation coefficient between 7 S and 10 S, shows a characteristic protein composition, with a major 73,000 MW polypeptide and some minor components. The results are discussed in view of a dynamic ribonucleoprotein structure.

Developmental changes in the protein and ribonucleic acid components of rat brain messenger ribonucleic acid-protein particles isolated from free polyribosomes by oligo(dT)-cellulose chromatography

A study has been made of the developmental changes that occur in the RNA and protein moieties of mRNA-protein particles isolated from newborn and adult rat forebrain free polyribosomes. mRNA-protein particles were isolated by oligo(dT)-cellulose chromatography from salt-washed polyribosomes dissociated by puromycin/0.5 M-KCl treatment as two fractions (E1 and E2) by using Tris/HCl/NaCl eluting buffers containing respectively 25 and 50% (v/v) formamide. Isopycnic centrifugation on CsCl gradients showed that the newborn-derived fractions E1 and E2 has buoyant densities of 1.48--1.50 and 1.41--1.43 g/cm3. Adult-derived E1 and E2 fractions had corresponding values of 1.47 and 1.42 g/cm3. The pooled mRNA-protein particles from the E1 and E2 fractions after deproteinization with proteinase K sedimented with a mean size of approx. 18 S on a sucrose gradient containing 85% formamide with little differences between mRNA molecules from newborn and adult. The mean lengths of the poly(A) segments were similar, being about 130 nucleotides long. Distinct changes were found in the protein composition of the mRNA-protein particles. Fractions E1 and E2 from the newborn contained two major proteins of mol.wts. 74 000 and 52 000 with differences in the relative proportions in each fraction. In contrast, adult fractions E1 and E2 contained predominantly the larger protein. However, the adult fraction E2 contained a more heterogeneous population of minor bands of proteins, including that of mol.wt. 52 000. The findings are discussed briefly in relation to other changes in the developing brain.

Messenger ribonucleoprotein complexes in human KB cells infected with adenovirus type 5 contain tightly bound viral-coded '100K' proteins

Late after infection of KB cells with adenovirus 5 an extra protein becomes associated with messenger ribonucleoprotein particles present in the polysomes. This protein has a molecular weight of 100000 and is identical to the virus coded '100K' protein found previously. The extra protein is firmly attached to the messenger ribonucleoprotein complexes. Its binding resists exposure to high salt concentrations as used in puromycin/high-salt dissociation and equilibrium centrifugation in Cs2SO4 gradients. In this respect it resembles the binding of two other proteins of Mr 74000 and 48000 which are commonly found in messenger ribonucleoprotein particles of various eukaryotic cells. The identity between the messenger ribonucleoprotein protein of Mr 100000 and the "100K' protein present in the soluble part of the cytoplasm was established by sodium dodecylsulphate/polyacrylamide gel electrophoresis, isoelectric focusing and peptide mapping after limited proteolysis with Staphylococcus aureus protease.

Characterization of the protein moiety of messenger ribonucleoprotein complexes from duck reticulocytes by two-dimensional polyacrylamide gel electrophoresis

The protein moiety of duck globin messenger ribonucleoprotein complexes isolated by oligo(dT)-cellulose chromatography or by sucrose gradient centrifugation was analysed by two-dimensional polyacrylamide gel electrophoresis under conditions where the separation in the first dimension occurs according to charge and in the second according to molecular weight. By comparing the pattern of protein from the mRNA - protein complex with that of ribosomal subunits we found that two acidic proteins with an identical molecular weight of about 49 000 and three basic proteins of about Mr 56 000, 64 000 and 73 000 were associated with the duck globin mRNA but were absent from either puromycin/high-salt-derived or 'run-off' ribosomal subunits. The comparison of the proteins from the complex with mRNA with those found in the 0.5 M KCl wash, commonly used as the source of initiation factors, showed also that only the 49 000-Mr protein from the complex could possibly be present in the 0.5 M KCl wash of polyribosomes; proteins with mobilities similar to the other three proteins complexed with mRNA were not detected in the salt wash of polyribosomes.

Identification and isolation of protamine messenger ribonucleoprotein particles from rainbow trout testis

Treatment of rainbow trout testis polyribosomes with ethylenediaminetetraacetic acid released polyadenylated protamine messenger RNA in the form of a ribonucleoprotein (mRNP) particle. This mRNP particle which sedimented at 12-14 S could be identified by hybridization to [3H]poly(U) and was partially purified by two successive sucrose gradient sedimentations. When RNA was extracted from the mRNP particle and used as a template in the wheat germ cell-free protein synthesizing system the sole product of translation was protamine. Of this RNA, 30% contained poly(A) sequences and was shown to comigrate with polyadenylated protamine messenger RNA during polyacrylamide gel electrophoresis. When the proteins of the mRNP particle were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the two prominent polypeptides with apparent molecular weights of 73 000 and 29 000 appeared reproducibly. Treatment of trout testis polyribosomes with puromycin in the presence of 0.5 M KCl released a smaller (8-10S) mRNP particle which was similarly shown to contain protamine messenger RNA. Trout testis postribosomal supernatant fraction possessed 16-18S mRNP particles containing polyadenylated RNA which cosedimented with protamine messenger RNA when the particles were dissociated with sodium dodecyl sulfate.

Characterization of mRNA-protein complexes from mammalian cells

In a previous report we described the use of oligo(dT)-cellulose for the isolation of mRNA-protein complexes from EDTA-dissociated polysomes extracted from normally growing or adenovirus infected KB-cells (I). Experiments presented here provide evidence that proteins involved in these complexes bind specifically to mRNA since: a) the proteins and mRNA cosediment through sucrose gradients, b) they adsorb and elute from oligo(dT)-cellulose together, and c) analysis of the products from ribonuclease digestion experiments show that the poly (A) end and a separate small fraction of the mRNA are resistant to the enzymes and attached to protein.

Isolation of biologically active polysomal messenger ribonucleoprotein by centrifugation in cesium sulfate

The ribosomal fraction from HeLa cells treated at elevated temperature was centrifuged in Cs2SO4. 1. The bulk of the RNA labeled in the presence of a low dose of actinomycin D banded at p = 1.36 g/cm3. 2. This fraction contained heterogeneous RNA and proteins with molecular weights close to those of proteins found in polysomal messenger ribonucleoproteins. 3. This ribonucleoprotein bound ribosomes in conditions were deproteinized RNA did not. 4. The binding was inhibited by aurintricarboxylic acid, ethylene diamine tetraacetic acid and sodium deoxycholate, but not by Triton X-100.

Release of RNA--DNA-protein complex during differentiation of the water mould Allomyces arbuscula

A correlation between release of a nucleic acid protein complex into the external medium and sporangial differentiation was found. Conditions preventing differentiation also stopped the release. Lethal lysis is not involved in this release process. Extracellular nucleic acids are very heterogenous, consisting of nucleotides as well as acid-precipitable nucleic acids. RNA was found to be associated with proteins and a hetero-duplex RNA--DNA associated with this nucleoprotein. Some speculations are presented about possible correlation between the release of nucleoprotein complexes and the intracellular events of differentiation.

Isolation and characteristics of mRNPs associated with bound polyribosomes from the ewe lactating mammary gland

The dissociation of bound polyribosomes from ewe lactating mammary gland, by EDTA or Puromycin-KC1 treatment releases Messenger Ribonucleoprotein particles (mRNP'S) which sediment in sucrose gradients as a single component having a sedimentation coefficient of about 22S. RNAs derived from mRNPs sediment between 9S and 15S and direct the synthesis of milk proteins in reticulocyte cell free systems. The mRNP protein moiety contains two major polypeptides with molecular weights of 52,000 and 72,000 daltons and two minor polypeptides with apparent molecular weights of 58,000 and 60,000 daltons.

EDTA-and puromycin-derived duck- and rabbit globin-messenger ribonucleoprotein complexes isolated by oligo (dT)-cellulose chromatography

Duck- and rabbit globin messenger ribonucleoprotein complexes isolated by oligo(dT) cellulose chromatography reveal an identical protein pattern-two main proteins of molecular weights of 73,000 and 49,000 daltons and minor components-whether the complexes have been liberated from polyribosomes with the EDTA- or the puromycin-high-salt method. In the globin messenger ribonucleoprotein particles of both species predominantly the protein with a molecular weight of 73,000 daltons is attached to poly(A)-containing regions of the messenger RNAs.