Biomedical subjects

F Shu

Publications and source records attributed to F Shu.

8 recordsLinked to original sources

PubMed1997

Histone-like transcription factors in eukaryotes.

Histone proteins have long been recognized as important regulators of eukaryotic gene expression. Condensation of DNA into chromatin by the core (H2A, H2B, H3, H4) and linker (H1, H5) histones effectively represses transcription initiation from the promoters of genes that have been packaged. Recently, eukaryotic transcriptional activators and coactivators (both positive and negative) resembling core and linker histone proteins have been discovered. Substantial progress has been made on structural and mechanistic studies of histones and histone-like transcription factors. Three-dimensional structures solved include the core histone octamer, an archael histone homodimer, two core histone-like subunits of transcription factor IID, a linker histone, and a linker histone-like transcriptional activator.

Amino Acid Sequence↗

PubMed1997

Combined radiofrequency ablation-cooling catheter for reversible cryothermal mapping and ablation.

Reversible cryothermal mapping of cardiac arrhythmias has been performed intraoperatively. However, a steerable cooling catheter for reversible mapping has not yet been developed. We therefore developed and tested a cooling system consisting of a -15 degrees C hypertonic saline reservoir and a 7F steerable catheter also capable of radiofrequency (RF) ablation. Using excised ovine hearts placed in a 37 degrees C circulating saline bath, we measured the temperatures at depths of 0 mm, 1 mm, and 2 mm. The temperature after 90 seconds of cooling was 16.5 +/- 2.1 degrees C at 0 mm compared to 23.9 +/- 4.1 degrees C at 1 mm and 31.1 +/- 3.9 degrees C at 2 mm depth (p < 0.01). These data suggest that a 7F steerable combined RF ablation-cooling catheter may achieve temperatures suitable for mapping arrhythmias such as atrial tachycardias and right ventricular outflow tract tachycardias. Further enhancements to achieve lower temperatures at depth may be needed to reversibly map other arrhythmias such as left ventricular tachycardias.

Animals↗

PubMed1997

B cell development in mice.

The development and establishment of the B Cell Repertoire is the net result of both genetic and environmental forces. The primary event at the genetic level is Ig gene rearrangement resulting in numerous possible combination of genes which can be further modified by somatic events such as N segment addition and somatic mutation. Environmental forces in the form of self and exogenous Ags also shape the repertoire by positively or negatively selecting B cells according to the specificity of their Ig receptors. These are dynamic processes beginning with the earliest expression of immunoglobulins in fetal life and continuing throughout life. In this review we discuss the genetic and selective mechanisms responsible for differences in the early immune system compared to that of the adult.

Animals↗

PubMed1996

High-level expression and deuteration of sperm whale myoglobin. A study of its solvent structure by X-ray and neutron diffraction methods.

Neutron diffraction has become one of the best ways to study light atoms, such as hydrogens. Hydrogen however has a negative coherent scattering factor, and a large incoherent scattering factor, while deuterium has virtually no incoherent scattering, but a large positive coherent scattering factor. Beside causing high background due to its incoherent scattering, the negative coherent scattering of hydrogen tends to cancel out the positive contribution from other atoms in a neutron density map. Therefore a fully deuterated sample will yield better diffraction data with stronger density in the hydrogen position. On this basis, a sperm whale myoglobin gene modified to include part of the A c11 protein gene has been cloned into the T7 expression system. Milligram amounts of fully deuterated holo-myoglobin have been obtained and used for crystallization. The synthetic sperm whale myoglobin crystallized in P2(1) space group isomorphous with the native protein crystal. A complete X-ray diffraction dataset at 1.5A has been collected. This X-ray dataset, and a neutron data set collected previously on a protonated carbon-monoxymyoglobin crystal have been used for solvent structure studies. Both X-ray and neutron data have shown that there are ordered hydration layers around the protein surface. Solvent shell analysis on the neutron data further has shown that the first hydration layer behaves differently around polar and apolar regions of the protein surface. Finally, the structure of per-deuterated myoglobin has been refined using all reflections to a R factor of 17%.

Animals↗

PubMed1995

Development of the mouse B-cell repertoire.

The mouse B-cell repertoire early in ontogeny contains B cells with receptor immunoglobulins exhibiting high connectivity, multi/self-reactivity, and generally low affinity. This is due structurally to extensive restriction in the germline components used to generate the B-cell receptor. The selective pressure acting on the nascent repetoire has both negative and positive components as seen in our in vivo models. VH81X-bearing B cells from the VH81X transgenic mice (and probably from normal mice) are subject to self-selective pressure with two components: a positive one favoring a certain (self-reactive) specificity in the CD23-IgM+ population and a negative one preventing the entry of B cells with this specificity into the CD23+IgM+ compartment.

Animals↗

PubMed1995

X-ray crystallography shows that translational initiation factor IF3 consists of two compact alpha/beta domains linked by an alpha-helix.

The structures of the two domains of translational initiation factor IF3 from Bacillus stearothermophilus have been solved by X-ray crystallography using single wavelength anomalous scattering and multiwavelength anomalous diffraction. Each of the two domains has an alpha/beta topology, with an exposed beta-sheet that is reminiscent of several ribosomal and other RNA binding proteins. An alpha-helix that protrudes out from the body of the N-terminal domain towards the C-terminal domain suggests that IF3 consists of two RNA binding domains connected by an alpha-helix and that it may bridge two regions of the ribosome. This represents the first high resolution structural information on a translational initiation factor.

Amino Acid Sequence↗

PubMed1995

Prokaryotic translation initiation factor IF3 is an elongated protein consisting of two crystallizable domains.

We show that translation initiation factor IF3 can be split into two fragments of nearly equal size by the Escherichia coli outer membrane protease omptin. Circular dichroism and small-angle neutron scattering show that the two fragments are structured as domains. Each domain is relatively compact, and they are separated by about 45 A in intact IF3. Thus IF3 is an elongated protein that consists of two well-separated domains. We suggest that these two domains are involved in ribosome binding across the cleft of the 30S ribosome. We also report the crystallization of each domain of IF3.

Circular Dichroism↗

PubMed1992

The fetal omentum in mice and humans. A site enriched for precursors of CD5 B cells early in development.

From these studies the fetal omentum appears to be an important site of B-cell generation in humans and a source of CD5 B cells in mice. We have analyzed the fetal omentum in other species and have found that B-cell development as determined by the presence of cytoplasmic IgM+ pre-B cells is also detected in the fetal rabbit omentum. We do not know if there is bias towards the production of CD5 B cells in this species; however, these preliminary results demonstrate that this site may be conserved throughout evolution in mammals as a site of B-cell generation. Because the fetal liver is also a source of precursors that can reconstitute this B-cell subset, what is the relationship between omentum and liver during the development of Ly-1 B cells? The most obvious relationship between these two sites is that cells simply migrate from one location to the other; that is, precursor cells may migrate from the fetal liver into the fetal omentum and in this milieu give rise to exclusively Ly-1+ B cells or the sister population. Alternatively, precursors of Ly-1 B cells may arise in the omentum and migrate to the liver. This is demonstrated graphically in the diagram (Fig. 6a) of a transverse section through an 8-week human fetus. In this paper, however, we suggest a model for the development of Ly-1+ B cells from the omentum and liver in which Ly-1 B cells arise from distinct precursors located in situ in the mesodermally derived omentum and mesothelial-derived liver capsule. The omentum primordia forms as the back to back fusion of the mesodermally derived lining of the peritoneal cavity, and this lining surrounds the developing gut when the liver begins to develop as an outgrowth of the intestinal primordia at approximately 3.5 weeks gestation; the outer covering or capsule of the liver is derived from the same tissue of origin as the omentum. Figure 6B is a diagram of a section through the same plane as Figure 6A but the body wall has been omitted. We propose that the Ly-1+ B cells arise in situ in the omentum and lining of the liver as indicated in Figure 6B. That Ly-1+ B cells arise from distinct precursors has been suggested by others, but ours is the first evidence for a developmental site that apparently contains B-cell progenitors for this B-cell subset.

Animals↗