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T Moss

Publications and source records attributed to T Moss.

At least 91 records · Page 5Linked to original sources
PubMed1987

The enhancement of ribosomal transcription by the recycling of RNA polymerase I.

It has been suggested that the tandemly repeated ribosomal genes of eukaryotes may be subject to a special mechanism of transcriptional enhancement, called Readthrough Enhancement, in which transcription factors are recycled. Recent experiments with the mouse ribosomal genes, although consistent with this possibility, were unable to distinguish between true Readthrough Enhancement and promoter occlusion. To test directly for Readthrough Enhancement, the pre-ribosomal RNA of Xenopus laevis was prematurely terminated within the 18S gene on a circular template. This premature termination was found to reduce the efficiency of pre-ribosomal RNA promotion in cis by 80 to 90%. Since the pre-ribosomal RNA is normally terminated only 213 base pairs upstream of its own initiation site, the results strongly suggest that the recycling of RNA polymerase, or Readthrough Enhancement, is a means by which ribosomal transcription is enhanced in Xenopus laevis.

Animals↗
PubMed1987

A complex array of sequences enhances ribosomal transcription in Xenopus laevis.

The ribosomal DNA spacer in Xenopus laevis was shown in previous studies to be involved in regulating the expression of the ribosomal genes. Here transcription enhancement by this spacer has been studied in some detail, to fully identify the sequences involved and to determine their relative importance in this phenomenon. It is shown that the 60/81 base-pair (bp) repeats, which were reported to be enhancer elements, act as part of a mode of enhancement whose effect is amplified by the spacer promoters or Bam islands. The "Bam super repeat", a combination of spacer promoter and 60/81 bp elements, is the major enhancer unit. Within a Bam super repeat, a near linear correlation between the number of 60/81 bp elements and enhancer activity is observed. Thus, there is no significant co-operativity in the binding of transcription factors to an array of these elements. Multiple Bam super repeats do not act additively and may actually interfere with each others action. Surprisingly this effect is observed both in the presence and absence of active spacer promoters. Sequences between the 3' end of the 28 S coding region and the first spacer promoter may also be involved in enhancement but only in a very minor fashion. In confirmation of recent studies, the presence of the unique ribosomal termination sequence, 213 bp upstream from the pre-rRNA initiation site, is essential for efficient promotion, as deletion of this sequence virtually abolishes pre-rRNA- transcription. These data are discussed in terms of the possible mechanisms of transcription enhancement.

Animals↗
PubMed1987

X-linked bulbo-spinal neuronopathy: a family study of three patients.

The clinical features of two brothers and one nephew with X-linked recessive bulbo-spinal neuronopathy are described. The neurophysiological investigations and sural nerve biopsy, previously unreported, confirmed that both motor and sensory nerves are affected. Because of the genetic implications, the importance is stressed of recognising this disorder as a separate entity which should not be classified with the spinal muscular atrophies.

Adult↗
PubMed1987

Gadolinium-labeled liposomes: targeted MR contrast agents for the liver and spleen.

A contrast agent for use in magnetic resonance (MR) imaging of the liver and spleen has been designed in which gadolinium-DTPA is chemically incorporated into the lamellar phase of liposome particles. This agent has excellent in vivo stability and is taken up by liver and spleen of normal mice after intravenous administration. The T1 increased by 110% in liver and 66% in spleen at 4 degrees C. At 37 degrees, the relaxation rate in the liver increased by 180%. This method is an attractive concept for the development of various organ-specific liposomal contrast agents that may be used for either MR imaging or nuclear medicine.

Animals↗
PubMed1986

The ribosomal spacer in Xenopus laevis is transcribed as part of the primary ribosomal RNA.

S1 mapping of Xenopus laevis ribosomal RNA transcripts, both in oocyte microinjection experiments and in vivo, shows that all but 212 bp of the so-called "non-transcribed" spacer (NTS) of the ribosomal DNA repeat is transcribed as part of the primary ribosomal transcript. The 40S pre-ribosomal RNA (pre-rRNA) is therefore a processing intermediate. The primary ribosomal transcript co-terminates with the previously described spacer transcripts [Moss], at a site 213 bp upstream of the 40S pre-rRNA initiation site. This mode of transcription suggests a simple mechanism for the recently proposed phenomenon of "readthrough-enhancement", [Moss et al, Moss], where readthrough transcription from an upstream gene may enhance transcription of a gene immediately downstream in the tandem ribosomal repeat.

Animals↗
PubMed1986

Spacer promoters are essential for efficient enhancement of X. laevis ribosomal transcription.

The X. laevis ribosomal DNA spacer contains duplicated RNA polymerase I "spacer promoters" and an array of repeated 60/81 bp promoter-related sequences. The latter have been shown to enhance transcription from a 40S preribosomal RNA promoter in cis. Here we present evidence that at least one spacer promoter is also necessary for efficient enhancement. Deletion of the spacer promoter sequences in a construct carrying only one such promoter reduces 40S RNA transcription to approximately 10% of wild type. This effect apparently is caused by inactivation of the spacer promoter, since mutants in which 4-177 bp of the spacer promoter and adjacent sequences are deleted are functionally equivalent. Spacer promoters and 60/80 bp arrays therefore probably act together to enhance 40S pre-RNA transcription in X. laevis.

Animals↗
PubMed1986

Metastasizing meningioma.

A very unusual case of metastatic spread of a meningioma is described. The clinical presentation was of extradural spinal cord compression, without evidence of a primary tumor. Computed tomography did not reveal any intracranial meningioma; the histopathology of the extradural spinal tumor was identical with that of two intracranial meningiomas previously excised.

Adult↗
PubMed1982

Transcription of cloned Xenopus laevis ribosomal DNA microinjected into Xenopus oocytes, and the identification of an RNA polymerase I promoter.

Transcription of a cloned Xenopus laevis ribosomal DNA (rDNA) fragment, microinjected into Xenopus oocytes, is initiated at the in vivo 40S pre-ribosomal RNA (pre-rRNA) site (+/- 2 bp) by RNA polymerase I. An X. laevis RNA polymerase I promoter has been mapped by studying the transcription of in vitro rDNA mutants in the oocyte system. The active promoter lies within the DNA segment beginning 145 bp upstream, and most probably ending 16 bp downstream, from the 40S pre-rRNA initiation site (-145 bp to +16 bp). Furthermore, active promoter elements lie more than 35 bp upstream from the initiation site (-35 bp). The X. laevis RNA polymerase I promoter therefore lies mainly upstream from the 40S pre-rRNA initiation site. Independent deletion of three adjacent rDNA segments lying between -61 and +16 bp reduces promoter activity by a factor of more than 16. The central of these "null" deletions removes an oligo(T)6 motif at -27 bp that is in an analogous position to the Goldberg-Hogness (TATA) box of RNA polymerase II promoters.

Animals↗
PubMed1980

More ribosomal spacer sequences from Xenopus laevis.

The base sequence analysis of a Xenopus laevis ribosomal DNA repeat (7) has been extended to cover almost the entire non-transcribed and external transcribed spacer. A compilation of these sequences is presented. All the repetitive and non-repetitive sequence elements of the spacer are identified and their evolution discussed. Comparison of the X.laevis and S.cerevisiae (25,26) ribosomal DNAs shows about 80% sequence conservation in the 18S gene but no sequence conservation, from the available data, in the external transcribed spacer. The sequence coding for the 3' terminus of the X.laevis 40S ribosomal precursor RNA is presented and its structural features analyzed.

Animals↗
PubMed1979

The putative promoter of a Xenopus laevis ribosomal gene is reduplicated.

With the aid of a novel poly-dA tailing-partial restriction technique and S1-protection mapping, the 5' terminal coding sequence for the 40S precursor ribosomal RNA of Xenopus laevis has been exactly identified. Since the promoter sequence for the 40S RNA should lie close to its 5' terminal coding sequence, we are able to conclude that the "Bam-Island" sequence reduplication (1) almost certainly represents a promoter reduplication.

Animals↗
PubMed1979

Sequence organization of the spacer DNA in a ribosomal gene unit of Xenopus laevis.

A detailed restriction map was constructed for a cloned Xenopus laevis rDNA fragment containing the nontranscribed spacer (NTS) and external transcribed spacer (ETS) together with a portion of both the 18S and 28S rRNA genes. The NTS was found to contain at least three distinct repetitious areas. Region 1 has a repeating unit of approximately 100 bp. The primary structure of this unit has been determined by DNA sequencing. Region 2 is very similar in organization to region 3, and both have an alternating 81/60 bp arrangement as revealed by restriction with Alu I and DNA sequencing. It can be shown that the 81 and 60 bp canons are virtually identical to one another excepting a deletion/insertion of a 21 bp segment. Region 3 differs from region 2 in having sites for Sma I with its 81 bp units. Between these repeated DNA sequences there are two identical, nonrepetitive DNA sequences, each of which is centered around a Bam Hl site. Most of the ETS has been sequenced. It was found to be nonrepetitive and extremely rich in Cs. Close to the 5' end of the 18S coding sequence there is a DNA stretch very rich in purines. About 2.25 kb upstream from the Eco Rl restriction site bisecting the 18S structural gene there is a unique sequence which may be homologous to the 5' end of the 40S precursor RNA. Present evidence suggests that the boundaries between NTS and ETS occur farther downstream than was suggested by electron microscopic data. Sequencing has revealed that the spacer DNA of X. laevis contains different kinds of simple DNA sequences, but no evidence has been found that spacer DNA once arose by saltation of a 15 bp segment. The most surprising finding was that the spacer sequences around the Bam restriction sites (the Bam islands) show high homology with a sequence near the NTS/ETS interface. From the restriction and sequencing analyses it can be deduced that in recent evolutionary times the DNA sequences near the 5' end of the ribosomal transcription unit were reduplicated twice and displaced into spacer by saltation of an intervening short DNA sequence (the 60/81 bp canons). Possible implications of these evolutionary events for spacer functions are consisdered. The sequencing has also provided a molecular basis for a whole range of conclusions arrived at previously by indirect approaches, and these are discussed.

Animals↗
PubMed1978

High-resolution proton-magnetic-resonance studies of chromatin core particles.

The binding of histones in chromatin core particles and in core particles depleted of histones H2A and H2B has been studied by high-resolution proton nuclear magnetic resonance (NMR) at 270 MHZ. At low ionic strengths it is shown that histones H3 and H4 are bound in the core particle. Further, whereas the apolar regions of H2A and H2B are also bound to the core particle, the basic N-terminal and C-terminal regions are more mobile and give rise to sharp resonances in the NMR spectrum of the core particle. Between 0.3 and 0.6 M NaCl there is further release of basic regions of histones H3 and H4 from the complex. The dissociation of the core particle between 0.6 and 2.0 M NaCl is accompanied by the release of the structured apolar regions of the histones as evidenced by the appearance of a complex aromatic spectrum and perturbed upfield ring-current-shifted methyl resonances. Arginine residues are implicated in the binding between histones and DNA and 69% of these residues are found in the apolar regions of the histones. The interactions between histones and DNA in the core particle thus involves H3 and H4 and the apolar regions of H2A and H2B. It is suggested that these basic regions of H2A and H2B have binding sites outside the core particle.

Animals↗
PubMed1978

Wandering.

Explore the source record for details and available documents.

Humans↗
PubMed1977

Sites of histone/histone interaction in the H3 - H4 complex.

Sites of interaction between histones H3 and h4 have been probed by investigating complex formation, firstly between histone H4 and three peptides cleaved by chemical means from histone H3 (residues 1-90 and 1-120 using cyanogen bromide and residues 42-135 using N-bromosuccinimide), secondly between histone H3 and two peptides cleaved from histone H4 (residues 1 - 84 using cyanogen bromide and residues 38-102 using chymotrypsin) and thirdly between the H4 peptide (residues 38-102) and the three H3 peptides (residues 1-90, 1-120 and 42-135). The criterion for complex formation is the appearance of characteristic perturbed resonances in the aromatic region of the 270 - MHZ proton resonance spectrum of the peptide mixture. It is concluded that loss of 37 N-terminal residues from histone H4 and 41 N-terminal residues from histone H3 does not prevent complex formation, whilst the loss of 18 C-terminal residues from H4 and 45 C-terminal residues from H3 does prevent it; that last 15 C-terminal residues of H3 are, however, not required for forming a complex. The regions important for complex formation are therefore defined as residues 42-120 in histone H3 and residues 38-102 in histone H4.

Amino Acids↗
PubMed1977

Studies on the role and mode of operation of the very-lysine-rich histone H1 in eukaryote chromatin. The three structural regions of the histone H1 molecule.

Limited digestion with trypsin of both calf thymus H1 histone and the fragment 1--120 of the H1 molecule has resulted in the isolation of the fragment 35--120. This fragment assumes a globular structure under physiological conditions of pH and ionic strength. The variable N-terminal portion of the molecule, up to residue 34, is not required for the formation of the H1 globular structure. Proton nuclear magnetic resonance (NMR) and ultracentrifugation studies show that the H1 histone molecule consists of three distinct structural domains under structuring conditions: a random coil 'nose' consisting of 35 to 40 residues from the N-terminal end; a globular 'head' involving the next approximately 80 residues; and a random-coil 'tail' of the remainder of the molecule.

Amino Acids↗