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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We used micrococcal nuclease to separate murine erythroleukemia cell (MELC) chromatin into soluble and insoluble fractions which differ in gene content and chromatin structure. Genes that are not expressed in the erythroid lineage, such as the Ig alpha and albumin genes, distribute preferentially into the soluble rather than the insoluble fraction, and are organized into nucleosomes in both fractions. Both alpha 1- and beta maj-globin genes are enriched in the insoluble fraction and are organized into structures that are partially devoid of nucleosomes in uninduced MELC, when the genes are transcriptionally inactive. Following chemical induction of MELC and the onset of globin gene transcription, globin gene enrichment and nucleosome disruption in the insoluble chromatin fraction increase. Using seven DNA subclones that span the beta maj-globin gene we show that insolubility and nucleosome disruption are largely limited to DNA sequences lying within the transcribed domain. Non-transcribed, flanking sequences are soluble and organized into nucleosomes. In addition, the globin genes found in insoluble, non-nucleosomal chromatin contain previously engaged RNA polymerases which can elongate globin RNA chains in vitro in a pattern qualitatively and quantitatively similar to intact nuclei. These results are discussed in terms of a model for globin gene activation during erythropoeisis.
J Mol Biol 1985 Mar 05
PMID:Nucleosome disruption precedes transcription and is largely limited to the transcribed domain of globin genes in murine erythroleukemia cells. 258 37

A variety of studies have documented multireactive antibodies in both the preimmune and naturally activated repertoire, but the relationship of these primarily IgM multireactive antibodies to antigen-specific primary and secondary response antibodies is currently not defined. In order to characterize the BALB/c preimmunization specificity repertoire and the baseline of naturally activated antibodies from which the immune response to a specific antigen (hen egg-white lysozyme, HEL) develops, panels of polyclonally activated blast-derived hybridomas (BlAbs) and natural antibody hybridomas (NAbs) from the spleens of unimmunized mice were screened for binding to a panel of nine complex antigens. Over half of the IgM-secreting BlAbs produced antibodies that were antigen-reactive; of these, over half were multireactive, i.e. capable of binding more than one complex antigen. There was no bias towards self vs foreign or thymus-dependent vs thymus-independent antigens. The frequency of antigen-reactive NAbs was about half the frequency of antigen-reactive antibodies found among the BlAbs. However, over half of the antigen-reactive NAbs were also multireactive, and the reactivity profile within the antigen-reactive subset of NAbs was similar to that within the antigen-reactive subset of BlAbs. These results suggest that the available repertoire of adult spleen cells contains a high proportion of multireactive antibodies, and that a subset of the available repertoire is randomly activated, yielding a small proportion of natural antibodies which closely reflect a random sampling of the available repertoire. Although monospecific precursor cells are rare, monospecific IgM BlAbs were found for all antigens in the panel except staphylococcal nuclease and mouse IgG. Monospecific as well as multireactive HEL-binding BlAbs were found at frequencies comparable to other protein antigens in the panel, and HEL-reactive NAbs were also present. On the other hand, it has previously been shown that HEL-reactive IgM antibodies (including multireactive antibodies whose specificities include HEL) are rare or absent in both the primary and secondary response to HEL. This cannot be attributed to an absence of available precursor B cells, and most likely reflects an early recruitment of HEL-reactive clones into the peripheral B cell pool. The possibility that polyreactive B cells may serve as precursors for some HEL-specific IgG antibodies is discussed.
Mol Immunol 1989 Oct
PMID:A substantial proportion of the adult BALB/c available B cell repertoire consists of multireactive B cells. 259 17

Digestion of nuclear chromatin of Trypanosoma brucei brucei procyclic culture forms with micrococcal nuclease yielded DNA fragments which formed DNA ladders in agarose gels, similar to those of rat liver. However, the chromatin of trypanosomes was digested more rapidly. The digestion of T. b. brucei chromatin yielded a large amount of DNA fragments of core-particle size. The numbers of base pairs per nucleosomal and linker DNA were identical in both species, if the digestion conditions were reduced in the case of T. b. brucei. Psoralen cross-linking of soluble chromatin of trypanosomes at 5 mM salt at pH 7 or pH 10 resulted in an irregular array of single-stranded (ss) bubbles separated by variable stretches of double-stranded (ds) DNA. The proportion of ss DNA was low compared with the ratio of ss/ds stretches in rat liver chromatin, which also showed regularly arranged nucleosomal DNA. Soluble chromatin of T. b. brucei, pre-treated with 500 mM NaCl to remove a potential H1 and psoralen cross-linked at 5 mM salt at pH 7 or pH 10 was to a great extent ds in both situations. The true nucleosome filament organization of T. b. brucei chromatin could only be shown by psoralen cross-linking the DNA in whole nuclei under physiological conditions. The results indicate that the chromatin of procyclic T. b. brucei differs significantly in its compaction pattern from rat liver chromatin; a typical histone H1 is not found, and the DNA-protein interactions are also less stable and can more easily be destabilized by experimental conditions.
Mol Biochem Parasitol 1989 Dec
PMID:Instability of the nuclear chromatin of procyclic Trypanosoma brucei brucei. 260 98

Conversion of the positioned nucleosome array characteristic of the repressed GAL1-GAL10 promoter region to the more accessible conformation of the induced state was found to depend on the upstream activation sequence, GAL4 protein, a positive regulator of transcription, and galactose, the inducing agent. The effect of the GAL4 protein-upstream activation sequence complex on the structure of adjacent chromatin required no other promoter sequences. Although sequences protected by histones in the repressed state became more accessible to micrococcal nuclease and (methidiumpropyl-EDTA)iron(II) cleavage following induction of transcription, DNA-protein particles containing these sequences retained the electrophoretic mobility of nucleosomes, indicating that the promoter region can be associated with nucleosomes under conditions of transcription activation.
Mol Cell Biol 1989 Apr
PMID:Upstream activation sequence-dependent alteration of chromatin structure and transcription activation of the yeast GAL1-GAL10 genes. 265 4

We have established an experimental system for reconstitution of an individual nucleosome on a closed DNA microdomain (operationally defined as a DNA domain of a size so small as to be unable to establish titratable superhelical turns). The microdomain (185 base-pairs (bp), composed of 128 bp encompassing the central part of the Saccharomyces cerevisiae ADH II promoter plus 57 bp of a polylinker) was obtained by ligation under conditions that produced three circularized forms characterized by different linkage numbers. These linkomers were tested for nucleosome reconstitution with S. cerevisiae histones. It was observed that only microcircles with linkage reduction (delta Lk = 1 or 2) could form a nucleosome, as defined by protection of a 145(+/- 2) bp DNA fragment from micrococcal nuclease, relaxed forms (open or closed circles) could not.
J Mol Biol 1989 Jun 05
PMID:Linkage reduction allows reconstitution of nucleosomes on DNA microdomains. 266 37

Isolated nuclei of Saccharomyces cerevisiae were incubated with five restriction nucleases. Out of the twenty-one recognition sequences for these nucleases in the centromere region of chromosome XIV, only five are accessible to cleavage. These sites map 11 bp and 74 bp to the left and 27 bp, 41 bp and 290 bp to the right, respectively, of the boundaries of the 118 bp functional CEN14 DNA sequence. The distance between the sites accessible to cleavage and closest to CEN14 is 156 bp, suggesting this is the maximal size of DNA protected in CEN14 chromatin. The DNA in CEN14 chromatin protected against cleavage with DNase I and micrococcal nuclease overlaps almost completely with this region. Hypersensitive regions flanking both sides are approximately 60 bp long. Analyses of other S. cerevisiae centromeres with footprinting techniques in intact cells or nucleolytic cleavages in isolated nuclei are discussed in relation to our results. We conclude that structural data of chromatin obtained with restriction nucleases are reliable and that the structure of CEN14 chromatin is representative for S. cerevisiae centromeres.
Mol Gen Genet 1989 Oct
PMID:Chromatin digestion with restriction endonucleases reveals 150-160 bp of protected DNA in the centromere of chromosome XIV in Saccharomyces cerevisiae. 269 39

DNA originating from chicken erythrocyte mononucleosomes was cloned and sequenced. The properties of nucleosome reconstruction were compared for two cloned inserts, selected on account of their interesting sequence organization, length and difference in DNA bending. Cloned fragment 223 (182 base-pairs) carries alternatively (A)3-4 and (T)4-5 runs approximately every ten base-pairs and is bent; cloned fragment 213 (182 base-pairs) contains a repeated C4-5ATAAGG consensus sequence and is apparently not bent. Our experiments indicate the preference of the bent DNA fragment 223 over fragment 213 to associate in vitro with an octamer of histones under stringent conditions. We provide evidence that the in vitro nucleosome formation is hampered in the case of fragment 213, whereas the reconstituted nucleosomes were equally stable once formed. For the correct determination of the positioning of the histone octamer with regard to the two nucleosome-derived cloned DNA sequences, the complementary use of micrococcal nuclease, exonuclease III and DNase I is a prerequisite. No unique, but rotationally related, positions of the histone octamer were found on these nucleosome-derived DNA fragments. The sequence-dependent anisotropic flexibility, as well as intrinsic bending of the DNA, resulting in a rotational setting of the DNA fragments on the histone core, seems to be a strong determinant for the allowed octamer positions, Exonuclease III digestion indicates a different histone-DNA association when oligo(d(C.G)n) stretches are involved. The apparent stagger near oligo(d(A.T)n) stretches generated by DNase I digestion on reconstituted nucleosome 223 was found to be inverted from the normal two-base 3' overhang to a two-base 5' overhang. Two possibilities of the oligo(d(A.T)n) minor groove location relative to the histone core are envisaged to explain this anomaly in stagger.
J Mol Biol 1989 May 05
PMID:Formation, stability and core histone positioning of nucleosomes reassembled on bent and other nucleosome-derived DNA. 273 23

The turnover rates of some mRNAs vary by an order of magnitude or more when cells change their growth pattern or differentiate. To identify regulatory factors that might be responsible for this variability, we investigated how cytosolic fractions affect mRNA decay in an in vitro system. A 130,000 X g supernatant (S130) from the cytosol of exponentially growing erythroleukemia cells contains a destabilizer that accelerates the decay of polysome-bound c-myc mRNA by eightfold or more compared with reactions lacking S130. The destabilizer is deficient in or absent from the S130 of cycloheximide-treated cells, indicating that it is labile or is repressed when translation is blocked. It is not a generic RNase, because it does not affect the turnover of delta-globin, gamma-globin, or histone mRNA and does not destabilize a major portion of polysomal polyadenylated mRNA. The destabilizer accelerates the turnover of the c-myc mRNA 3' region, as well as subsequent 3'-to-5' degradation of the mRNA body. It is inactivated in vitro by mild heating and by micrococcal nuclease, suggesting that it contains a nucleic acid component. c-myb mRNA is also destabilized in S130-supplemented in vitro reactions. These results imply that the stability of some mRNAs is regulated by cytosolic factors that are not associated with polysomes.
Mol Cell Biol 1989 May
PMID:Regulation of c-myc mRNA stability in vitro by a labile destabilizer with an essential nucleic acid component. 274 42

The Xenopus oocyte supernatant (oocyte S-150) forms chromatin in a reaction that is affected by temperature and by the concentration of ATP and Mg. Under optimal conditions at 27 degrees C, relaxed DNA plasmids are efficiently assembled into supercoiled minichromosomes with the endogenous histones H3, H4, H2A and H2B. This assembly reaction is a gradual process that takes four to six hours for completion. Micrococcal nuclease digestions of the chromatin assembled under these conditions generate an extended series of DNA fragments that are, on average, multiples of 180 base-pairs. We have examined the effect of histone H1 in this system. Exogenous histone H1, when added at a molar ratio of H1 to nucleosome of 1:1 to 5:1, causes an increase in the micrococcal nuclease resistance of the chromatin without causing chromatin aggregation under these experimental conditions. Furthermore, the periodically arranged nucleosomes display longer internucleosome distances, and the average length of the nucleosome repeat is a function of the amount of histone H1 added, when this histone is present at the onset of the assembly process. In contrast, no major change in the length of the nucleosome repeat is observed when histone H1 is added at the end of the chromatin assembly process. Protein analyses of the purified minichromosomes show that histone H1 is incorporated in the chromatin that is assembled in the S-150 supplemented with histone H1. The amount of histone H1 bound to chromatin is a function of the total amount of histone H1 added. We define here the parameters that generate histone H1-containing chromatin with native nucleosome repeats from 160 to 220 base-pairs, and we discuss the implications of these studies.
J Mol Biol 1989 Sep 05
PMID:Assembly and properties of chromatin containing histone H1. 281 Mar 66

Chromatin fragmentation of bovine peripheral blood lymphocytes from normal animals and the ones suffering from chronic lympholeucosis (CLL) by DNase I, micrococcal nuclease and purified Ca/Mg-dependent endonuclease from nuclei of human splenocytes was studied. The lymphocytes chromatin from CLL animals was shown to be more resistant to nucleases, than the one from normal animals. It was found that difference between fragmentation of chromatin samples from normal and CLL bovines was more dramatic when Ca/Mg- dependent endonuclease was used versus traditionally exploited DNase I and micrococcal nuclease. The data suggest that purified Ca/Mg-dependent endonuclease can be a useful enzymatic probe for detection of lymphocytes chromatin changes during CLL.
Mol Gen Mikrobiol Virusol 1987 Sep
PMID:[Ca/Mg-dependent endonuclease as a probe for detecting chromatin changes in lymphocytes in chronic lymphoid leukemia]. 282 38


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