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M T Murray

Publications and source records attributed to M T Murray.

10 recordsLinked to original sources
PubMed1995

A mouse homologue of the Xenopus germ cell-specific ribonucleic acid/deoxyribonucleic acid-binding proteins p54/p56 interacts with the protamine 2 promoter.

Recent evidence indicates that a member of the Y box-binding family of transcriptional regulators is identical to p56, a predominant protein of messenger ribonucleoprotein complexes. The p56 protein is highly enriched in oocytes and testis, and a functional RNA binding mouse cytoplasmic homologue has been cloned and partially characterized. Because few potential testis-specific transcriptional regulators have been identified, the testis-enriched Y box-binding proteins represent trans-acting elements of a unique model system for the study of haploid gene expression. The 5' flanking region of the testis-specific, haploid-expressed mouse protamine 2 gene contains an element with a 9-of-12 nucleotide identity with the previously defined Y box consensus sequence. We have investigated the possible role of Y box-binding proteins in transcriptional regulation of protamine 2 using specific antibodies and DNA-protein binding assays. Western blot analyses with two different anti-p54/p56 antibodies demonstrate that a mouse homologue of Xenopus p54/p56 is present in transcriptionally active mouse testis nuclear extracts. Our results further indicate that the Xenopus Y box-binding proteins bind to an element 5' to the mouse protamine 2 gene. Similarly, binding of the mouse testis homologue to the protamine 2 Y box element is demonstrated by gel mobility shift and antibody supershift analyses. The demonstrated interactions between testis-enriched Y box-binding proteins and protamine 2 transcriptional control elements therefore represent a unique system for functional studies to determine the mechanism of regulation of haploid gene expression.

Animals↗
PubMed1994

Nucleic acid-binding properties of the Xenopus oocyte Y box protein mRNP3+4.

Y box proteins contain the conserved cold shock domain (CSD) and several basic/aromatic (B/A) islands that are rich in arginine and aromatic residues. The binding of purified Xenopus oocyte 6S Y box protein, mRNP3+4, to Y box RNA, single-stranded (ss) DNA, and double-stranded (ds) DNA was studied by gel mobility shift and nitrocellulose filter binding assays. mRNP3+4 specifically bound Y box ssDNA or RNA, while binding of dsDNA was not detected. Y box ssDNA and RNA did not efficiently cross-compete for mRNP3+4 binding, and no evidence for ternary complex formation was detected. However, Y box ssDNA binding was competed by high concentrations of Y box RNA or nonspecific RNA competitors, indicating that the ssDNA-binding site has a lower affinity for RNA. mRNP3+4 demonstrated similar affinity for either Y box RNA or ssDNA. However, at elevated ionic strength RNA binding was markedly greater than ssDNA binding, indicating that RNA binding involves nonionic interactions that are not utilized for ssDNA binding. Recombinant polypeptides containing B/A islands bound Y box RNA exclusively, but inclusion of the CSD led to preferential ssDNA binding. The results demonstrate that the B/A islands are exclusively RNA-binding, while the CSD exhibits preferential binding of ssDNA. The inability of Y box RNA and ssDNA to efficiently cross-compete for mRNP3+4 binding suggests that isoforms exhibit preferential ssDNA or RNA binding.

Amino Acid Sequence↗
PubMed1993

Proteins homologous to the Xenopus germ cell-specific RNA-binding proteins p54/p56 are temporally expressed in mouse male germ cells.

Antibodies specific for the Xenopus oocyte cytoplasmic 6S mRNA-binding particle p54/p56 and antibodies against Xenopus germ cell DNA-binding protein FRG Y2 recognize two RNA-binding proteins of the mouse testis. The mouse testis proteins, estimated by SDS-PAGE to be about 48 and 52 kDa, form RNA-protein complexes with either translationally regulated or control RNAs, suggesting that they are sequence-independent RNA-binding proteins. The binding of the 48/52-kDa proteins to RNA is reduced by heparin. The expression of the 48/52-kDa mouse proteins is germ cell-specific and developmentally regulated in the testis with a maximal amount of the two proteins being detected in early postmeiotic cells (round spermatids), a cell type where many mRNAs are stored. The 48/52-kDa proteins are detected solely in the nonpolysomal fractions of postmitochondrial adult testis extracts and are not detected in extracts of brain, liver, or prepuberal testes from 12-day-old mice. We conclude that two RNA-binding proteins that appear to be immunological and functional homologues of the Xenopus germ cell-specific RNA/DNA-binding proteins p54/p56/FRG Y2 are present in male germ cells and form complexes with stored mRNAs.

Animals↗
PubMed1992

Sequence analysis of cytoplasmic mRNA-binding proteins of Xenopus oocytes identifies a family of RNA-binding proteins.

Storage of maternal mRNAs as nontranslated ribonucleoprotein (RNP) complexes is an adaptive strategy in various vertebrate and invertebrate oocytes, for rapid translational recruitment during embryonic development. Previously, we showed that Xenopus laevis oocytes have a soluble cytoplasmic pool of mRNA-binding proteins and particles competent for messenger RNP assembly in vitro. Here we report the isolation of cDNAs for the most abundant messenger RNPs, the 54- and 56-kDa polypeptide (p54/p56) components of the approximately 6S mRNA-binding particle, from an ovarian expression library. The nucleotide sequence of p56 cDNA is almost identical to that recently reported for the putative Xenopus transcription factor FRG Y2. p54 and p56 are highly homologous and are smaller than expected by SDS/PAGE (36 kDa and 37 kDa) due to anomalous electrophoretic mobility. They lack the "RNP consensus motif" but contain four arginine-rich "basic/aromatic islands" that are similar to the RNA-binding domain of bacteriophage mRNA antiterminator proteins and of tat protein of human immunodeficiency virus. The basic/aromatic regions and a second conspicuous 100-amino acid "domain C" of p54 and p56 are conserved in the following DNA-binding proteins: human proteins dpbA, dpbB, and YB-1, rat protein EFIA, and Xenopus protein FRG Y1, all reported to bind to DNA; domain C is homologous to the major Escherichia coli cold-stress-response protein reportedly involved in translational control. Antibodies raised against a peptide of domain C have identified similar proteins in Xenopus somatic cells and in some mammalian cells and tissues. We conclude that p54 and p56 define a family of RNA-binding proteins, at least some of which may be involved in translational regulation.

Amino Acid Sequence↗
PubMed1991

Different forms of soluble cytoplasmic mRNA binding proteins and particles in Xenopus laevis oocytes and embryos.

To gain insight into the mechanisms involved in the formation of maternally stored mRNPs during Xenopus laevis development, we searched for soluble cytoplasmic proteins of the oocyte that are able to selectively bind mRNAs, using as substrate radiolabeled mRNA. In vitro mRNP assembly in solution was followed by UV-cross-linking and RNase digestion, resulting in covalent tagging of polypeptides by nucleotide transfer. Five polypeptides of approximately 54, 56 60, 70, and 100 kD (p54, p56, p60, p70, and p100) have been found to selectively bind mRNA and assemble into mRNPs. These polypeptides, which correspond to previously described native mRNP components, occur in three different particle classes of approximately 4.5S, approximately 6S, and approximately 15S, as also determined by their reactions with antibodies against p54 and p56. Whereas the approximately 4.5S class contains p42, p60, and p70, probably each in the form of individual molecules or small complexes, the approximately 6S particles appears to consist only of p54 and p56, which occur in a near-stoichiometric ratio suggestive of a heterodimer complex. The approximately 15S particles contain, in addition to p54 and p56, p60 and p100 and this is the single occurring form of RNA-binding p100. We have also observed changes in the in vitro mRNA binding properties of these polypeptides during oogenesis and early embryonic development, in relation to their phosphorylation state and to the activity of an approximately 15S particle-associated protein kinase, suggesting that these proteins are involved in the developmental translational regulation of maternal mRNAs.

Animals↗
PubMed1987

Conservation of ferritin heavy subunit gene structure: implications for the regulation of ferritin gene expression.

Ferritin stores iron within a protein shell consisting of 24 subunits of two types, heavy (H) and light (L). According to Southern blotting, the rat genome contains four copies homologous to the H-subunit cDNA (H cDNA). To determine whether only one of these is expressed, H cDNAs isolated from rat liver and heart mRNAs were compared and found to share identical nucleotide sequences. Next, genomic clones for three of the four rat H-subunit loci were isolated. Two were classical processed pseudogenes, whereas the third contained an expressed gene. RNase intron mapping of this expressed gene generated the same exon protection pattern when total RNA from rat liver or heart was used, indicating that this gene accounts for most or all of the H-subunit mRNAs (H mRNAs) in these tissues. Comparison of the expressed rat H-subunit gene (H gene) structure with published sequences for other species displays considerable conservation. The coding sequence of the rat H gene predicts 95% similarity to the human amino acid sequence, thus being more highly conserved than the L-subunit sequence of these species. Near the cap region of the 5' untranslated region, the rat H mRNA displays a 28-nucleotide sequence that is almost totally conserved in the corresponding region of the human, bullfrog, and chicken H mRNA and is also faithfully represented in the rat and human L-subunit mRNAs (L mRNAs), thus making this sequence a prime candidate for involvement in the known translational regulation of both subunits by iron. In the 5' flanking region, partially conserved sequences common to H gene and L-subunit gene (L gene) of the rat may be involved in transcriptional regulation by iron, whereas those conserved only in the H gene of man and the rat imply that other factors may independently control H-subunit regulation.

Amino Acid Sequence↗
PubMed1985

Scanning electron microscopy of chronically stimulated platinum intracochlear electrodes.

Platinum electrodes were examined for evidence of corrosion using a scanning electron microscope (SEM). In vivo electrodes, stimulated using charge-balanced biphasic pulses for periods of up to 2000 h at charge densities of 0.18-0.32 microC mm-2 geom. per phase, were compared with in vitro electrodes stimulated in inorganic saline using similar stimulus parameters, and with in vivo control electrodes. The in vitro stimulated electrodes showed evidence of platinum corrosion at high charge density and aggregate charge injection. Significantly, the in vivo stimulated electrodes showed no evidence of stimulus induced corrosion. Indeed, their surfaces were similar to the in vivo control electrodes. In vitro electrochemical studies have demonstrated that proteins play a significant role in the inhibition of platinum dissolution: the present study has demonstrated an inhibitory effect in vivo. This may be due to the presence of proteins.

Animals↗
PubMed1984

Implanted material tolerance studies for a multiple-channel cochlear prosthesis.

We have performed a number of temporal bone and animal studies in order to evaluate the histopathological effects of intracochlear electrode implantation and chronic electrical stimulation. Our results indicate that (a) the insertion of a free-fit scala tympani array results in minimal damage to the membranous labyrinth; (b) the materials used in the electrode array evoke mild tissue reactions when implanted subcutaneously, in muscle, or within the scala tympani; (c) intracochlear electrical stimulation for periods of 500 to 2000 hours, using carefully controlled biphasic pulses, does not adversely affect the population or neural activity of the primary auditory neurones; (d) labyrinthine infection severely reduces the number of viable spiral ganglion cells; (e) an adequate fibrous tissue seal of the round window can prevent the spread of infection from the bulla to the implanted cochlea in cats, following inoculation of the bulla cavity with bacteria; (f) bone growth is not associated with electrical stimulation per se; (g) the electrode arrays show minimal platinum dissolution and no apparent degradation of the Silastic carrier following periods of long-term intracochlear electrical stimulation.

Animals↗
PubMed1982

Alterations in brain dopamine and GABA following inorganic or organic manganese administration.

Administration of manganese to mice in the form of MnCl2 (4%) in the diet for 6 months or injections of the organic fuel-additive methylcyclopentadienyl manganese tricarbonyl (MMT) for 3 weeks resulted in a decrease in dopamine concentrations in the striatum and olfactory tubercles. The GABA content of the striatum was elevated after either treatment while the cerebellar GABA content did not change; GABA in the substantia nigra of MMT-treated mice was also increased. Choline acetyltransferase activity remained unchanged in response to either manganese treatment. These results are in general agreement with previous studies of inorganic manganese toxicity in other animal species. These changes in neurotransmitter concentrations were observed after longterm manganese administration but were not seen in mice injected acutely with MMT or exposed to MnCl2 for 1-2 months.

Animals↗