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1181. Universal control mechanism regulating onset of M-phase.
The onset of M-phase is regulated by a mechanism common to all eukaryotic cells. Entry into M-phase is determined by activation of the p34cdc2 protein kinase which requires p34cdc2 dephosphorylation and association with cyclin.
1182. Signal transduction in bacteria.
Cells display a remarkable ability to respond to small fluctuations in their surroundings. In simple microbial systems, information from sensory receptors feeds into a circuitry of regulatory proteins that transfer high energy phosphoryl groups from histidine to aspartate side chains. This phosphotransfer network couples environmental signals to an array of response elements that control cell motility and regulate gene expression.
1185. Regulation of the mevalonate pathway.
The mevalonate pathway produces isoprenoids that are vital for diverse cellular functions, ranging from cholesterol synthesis to growth control. Several mechanisms for feedback regulation of low-density-lipoprotein receptors and of two enzymes involved in mevalonate biosynthesis ensure the production of sufficient mevalonate for several end-products. Manipulation of this regulatory system could be useful in treating certain forms of cancer as well as heart disease.
1186. Co-localization of molecules involved in antigen processing and presentation in an early endocytic compartment.
作者: L E Guagliardi.;B Koppelman.;J S Blum.;M S Marks.;P Cresswell.;F M Brodsky.
来源: Nature. 1990年343卷6254期133-9页
The pathways of intracellular traffic involved in antigen processing and presentation have been defined by immunoelectron microscopy. The export pathway for class II histocompatibility molecules and the antigen import pathway meet in a peripheral endocytic compartment having all the molecular machinery believed to be required for antigen processing and presentation, including internalized surface immunoglobulins, proteolytic enzymes and invariant chains. This compartment defines a site where peptides from endocytosed antigen can bind class II molecules en route to the cell surface for presentation to T cells.
1187. Conformations of immunoglobulin hypervariable regions.
作者: C Chothia.;A M Lesk.;A Tramontano.;M Levitt.;S J Smith-Gill.;G Air.;S Sheriff.;E A Padlan.;D Davies.;W R Tulip.
来源: Nature. 1989年342卷6252期877-83页
On the basis of comparative studies of known antibody structures and sequences it has been argued that there is a small repertoire of main-chain conformations for at least five of the six hypervariable regions of antibodies, and that the particular conformation adopted is determined by a few key conserved residues. These hypotheses are now supported by reasonably successful predictions of the structures of most hypervariable regions of various antibodies, as revealed by comparison with their subsequently determined structures.
1188. The GUS reporter gene system.
The GUS reporter gene system is already a powerful tool for the assessment of gene activity in transgenic plants. Further developments may lead to routine in vivo analysis and fusion genetics.
1190. A regulatory hierarchy for cell specialization in yeast.
The specialized sets of genes that determine different cell types in yeast are controlled by combinations of DNA-binding proteins some of which are present only in certain cell types whereas others are present in all cell types. Final differentiation requires an inductive signal that triggers both gene transcription and cell-cycle arrest. Synthesis of the proteins coded by the 'master regulatory' mating-type locus is regulated so as to generate a heterogeneous mitotic cell population containing a stem-cell lineage.
1191. Adaptation, speciation and hybrid zones.
Many species are divided into a mosaic of genetically distinct populations, separated by narrow zones of hybridization. Studies of hybrid zones allow us to quantify the genetic differences responsible for speciation, to measure the diffusion of genes between diverging taxa, and to understand the spread of alternative adaptations.
1192. How the ear's works work.
The senses of hearing and equilibrium depend on sensory receptors called hair cells which can detect motions of atomic dimensions and respond more than 100,000 times a second. Biophysical studies suggest that mechanical forces control the opening and closing of transduction channels by acting through elastic components in each hair cell's mechanoreceptive hair bundle. Other ion channels, as well as the mechanical and hydrodynamic properties of hair bundles, tune individual hair cells to particular frequencies of stimulation.
1193. Inositol phosphates and cell signalling.
Inositol 1,4,5-trisphosphate is a second messenger which regulates intracellular calcium both by mobilizing calcium from internal stores and, perhaps indirectly, by stimulating calcium entry. In these actions it may function with its phosphorylated metabolite, inositol 1,3,4,5-tetrakisphosphate. The subtlety of calcium regulation by inositol phosphates is emphasized by recent studies that have revealed oscillations in calcium concentration which are perhaps part of a frequency-encoded second-messenger system.
1196. Sex in flies: the splice of life.
The discovery that the primary transcripts of many genes are processed to produce more than one kind of messenger RNA focuses attention on the control of RNA processing as a developmental regulatory mechanism. In the fruit-fly Drosophila melanogaster, differential splicing of a hierarchy of regulatory genes determines sex, and thus the molecular biology of sex determination in the fruit-fly may lead to insights into the mechanisms by which alternative splicing is regulated.
1197. Retro-secretion of recombinant proteins.
The retroviral Gag protein can be used to package recombinant proteins produced by mammalian cell cultures. Protein products can then be isolated easily from the recombinant virions.
1199. The molecular control of cell division, differentiation commitment and maturation in haemopoietic cells.
Several glycoproteins that control blood-cell production and function have been purified and sequenced. The four colony-stimulating factors interact in a complex way to regulate the differentiation and maturation of the granulocyte and macrophage lineages and have potential applications for the clinical manipulation of blood-cell production.
1200. The search for the causes of breast and colon cancer.
Epidemiological studies of breast and colon cancers implicate diet as a causative factor but the evidence is stronger for colon cancer, the occurrence of which may be reduced by diets with less animal fat and more fruit and vegetables.
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