Biomedical subjects

B Hoffman-Liebermann

Publications and source records attributed to B Hoffman-Liebermann.

29 records · Page 2Linked to original sources

PubMed1986

Human homologs of TU transposon sequences: polypurine/polypyrimidine sequence elements that can alter DNA conformation in vitro and in vivo.

We previously have shown that homologs of the outer domain segment of the inverted repeat termini (IVR-OD) of the sea urchin TU transposons are conserved among multiple eucaryotic species, including humans. We report here that two cloned human DNA IVR-OD homologs, Hut2 and Hut17, consist of a series of tandem repeats of the trimer AGG/TCC, forming segments (313 and 221 base pairs in length, respectively) of polypurine/polypyrimidine (pPu/pPy or "Puppy") asymmetry in the two DNA strands; these are punctuated at certain sites with variant trimers, which are different for the two clones. Sequences homologous to the Hut2 pPu/pPy tract exist at multiple sites in the DNA of a wide variety of eucaryotes. Hybridization of human DNA with a Hut2 probe or with a previously described chicken DNA pPu/pPy sequence indicates that pPu/pPy sequences can be grouped into families distinguishable by the extent of their homology with each probe at different hybridization stringencies. Moreover, particular pPu/pPy tracts show species-specific differences in their distribution. Both the Hut2 and Hut17 pPu/pPy tracts are cleaved by S1 nuclease when tested on supercoiled plasmids. Most if not all of the 313-base-pair Hut2 pPu/pPy tract is also sensitive to S1 in its native location in HeLa cell chromatin, indicating that the sequence contains conformational information that can be expressed in vivo. This view is supported by evidence that exogenously derived Hut2 pPu/pPy tracts introduced into mouse L cells and integrated in chromatin can assume an S1-sensitive conformation.

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PubMed1985

Structure and unusual characteristics of a new family of transposable elements in the sea urchin Strongylocentrotus purpuratus.

The transposable element family TU of the sea urchin Strongylocentrotus purpuratus, a higher eucaryote, has recently been described (D. Liebermann, B. Hoffman-Liebermann, J. Weinthal, G. Childs, R. Maxson, A. Mauron, S.N. Cohen, and L. Kedes, Nature [London] 306:342-347, 1983). A member of this family, TU4, has an insertion, called ISTU4, of non-TU DNA. ISTU4 is a member of a family of repetitive sequences, which are present in some 1,000 copies per haploid S. purpuratus genome (B. Hoffman-Liebermann, D. Liebermann, L.H. Kedes, and S.N. Cohen, Mol. Cell. Biol. 5:991-1001, 1985). We analyzed this insertion to determine whether it is itself a transposable element. The nucleotide sequence of ISTU4 was determined and showed an unusual structure. There are four, approximately 150 nucleotides long, imperfect direct repeats followed by a single truncated version of these repeats. This region is bounded at either side by approximately 100-nucleotide-long sequences that are not related to each other or to the repeats. Nucleotide sequences at the boundaries of ISTU4-homologous and flanking regions in five genomic clones show that ISTU4 represents a family of sequences with discrete ends, which we call Tsp elements. We showed that the genomic locus that carries a Tsp element in one individual was empty in other individuals and conclude that Tsp elements are a new and different type of transposable element. Tsp elements lack two features common to most other transposable elements: Tsp integration does not result in the duplication of host DNA, and there are no inverted repeats at their termini, although short inverted repeats are present at a distance from the termini.

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PubMed1985

TU elements: a heterogeneous family of modularly structured eucaryotic transposons.

We describe here a family of foldback transposons found in the genome of the higher eucaryote, the sea urchin Strongylocentrotus purpuratus. Two major classes of TU elements have been identified by analysis of genomic DNA and TU element clones. One class consists of largely similar elements with long terminal inverted repeats (IVRs) containing outer and inner domains and sharing a common middle segment that can undergo deletions. Some of these elements contain insertions. The second class is highly heterogeneous, with many different middle segments nonhomologous to those of the first-class and variable-sized inverted repeats that contain only an outer domain. The middle and insertion segments of both classes carry sequences that also are found unassociated from the inverted repeats at many other genomic locations. We conclude that the TU elements are modular structures composed of inverted repeats plus other sequence domains that are themselves members of different families of dispersed repetitive sequences. Such modular elements may have a role in the dispersion and rearrangement of genomic DNA segments.

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PubMed1982

Regulation and role of different macrophage-and granulocyte-inducing proteins in normal and leukemic myeloid cells.

It has previously been shown that there are different molecular forms of macrophage-and granulocyte-inducing (MGI) proteins; one form, MGI-l, induced the formation of colonies with differentiated cells from normal myeloblasts and another form, MGI-2, induced normal differentiation in MGI+D+ leukemic myeloblasts that no longer require MGI-l to form colonies. The present results indicate that MGI-2 can also induce differentiation (without inducing colony formation) in the normal cells, and that MGI-l induced MIG-2 in the normal but not in the leukemic cells. It is suggested from these results that MGI-2 is the differentiation-inducing protein for normal and leukemic cells whereas MGI-l is the growth-inducing protein that induces colony formation by the normal cells, and that induction of differentiation in the normal cell colonies is due to induction of MGI-2 by MGI-l.

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PubMed1981

Regulation of gene expression by tumor promoters. III. Complementation of the developmental program in myeloid leukemic cells by regulating mRNA production and mRNA translation.

Regulation of gene expression has been analysed in different clones of mouse myeloid leukemic cells treated with the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA), the macrophage- and granulocyte-inducing protein MGI, and combined treatment with TPA and MGI. Two-dimensional gel electrophoresis was used to measure changes in the rate of synthesis of specific proteins and in the amount of corresponding translatable mRNAs assayed in the reticulocyte cell-free translation system. TPA induced different subsets of differentiation-associated protein changes in the different clones and the degree of response to TPA was not necessarily related to the degree of response to MGI. It is shown that TPA can induce protein changes either by inducing the synthesis of new mRNA, by increasing or decreasing the amount of pre-existing mRNA, or by modulating the translation of a constant amount of mRNA. Combined treatment with TPA and MGI resulted in an enhancement of protein changes induced by MGI or TPA alone and induced differentiation-associated protein changes not induced by either compound separately in differentiation-defective clones. This complementation of gene expression appeared to be due to each compound inducing functions not induced by the other, so that the combined treatment resulted in new gene expression. Complementation also occurred at the level both of mRNA production and of mRNA translation. It is suggested that the ability of TPA to regulate gene expression at the level of mRNA production and mRNA translation and to complement changes in gene expression induced by other compounds such as MGI are important functions for its role as a tumor promoter.

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PubMed1981