Structural implications of BER enzymes: dragons dancing--the structural biology of DNA base excision repair.
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The number of the complement component C4 genes varies from 2 to 8 in a diploid genome among different human individuals. Three quarters of the C4 genes in Caucasian populations have the endogenous retrovirus, HERV-K(C4), in the ninth intron. The remainder does not. The C4 serum proteins are highly polymorphic and their concentrations vary from 100 to approximately 1000 microg/ml. There are two distinct classes of C4 protein, C4A and C4B, which have diversified to fulfill (a) the opsonization/immunoclearance purposes and (b) the well-known complement function in the killing of microbes by lysis and neutralization, respectively. Many infectious and autoimmune diseases are associated with complete or partial deficiency of C4A and/or C4B. The adverse effects of high C4 gene dosages, however, are just emerging, as the concepts of human C4 genetics are revised and accurate techniques are applied to distinguish partial deficiencies from differential expression caused by unequal C4A and C4B gene dosages and gene sizes. This review attempts to dissect the sophisticated genetics of complement C4A and C4B. The emphases are on the qualitative and quantitative diversities of C4 genotypes and phenotypes. The many allotypic variants and the processed products of human and mouse C4 proteins are described. The modular variation of C4 genes together with the serine/threonine nuclear kinase gene RP, the steroid 21-hydroxylase CYP21, and extracellular matrix protein TNX (RCCX modules) are investigated for the effects on homogenization of C4 protein polymorphisms, and on the unequal genetic crossovers that knocked out the functions of CYP21 and/or TNX. Furthermore, the influence of the endogenous retrovirus HERV-K(C4) on C4 gene expression and the dispersal of HERV-K(C4) family members in the human genome are discussed.
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Most bacteria that colonize eukaryotes must bind directly to host cells to establish a replicative niche. In enteric bacteria, adhesion to host cells is often promoted by a lectin found on surface-localized pili. Some pili promote efficient adhesion only when they are subjected to shear stress, as found during the flow of blood over endothelium or mucous over the surface of the epithelium.
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Since early anatomical descriptions, the existence of dendritic spines has stimulated intense curiosity and speculation about their regulation and function. Research over the past three decades has described an impressive mutability in dendritic-spine number and morphology under a variety of physiological circumstances. Current evidence favors a proposed model in which two pools of actin filaments, one stable and the other dynamic, support both persistent spine structure and rapid spine motility. Potential functions of spine motility and dynamic actin include regulated protein scaffolding, retrograde signaling and synapse stabilization.
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AMPA receptors are tetramers assembled as a dimer-of-dimers with a 2-fold rotational symmetry in their extracellular domains. Two papers in this issue of Neuron, by Horning and Mayer and Sobolevsky et al., provide complementary data that extend this view and highlight the role of dimers in channel gating.
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MEDIAWATCH: Parts of the British media are keeping up a campaign against the introduction of genetically modified crops ahead of the governemnet's assessment of the trial programme this autumn, often to the detriment of the arguments.
Assembly of antigen-presenting complexes between class I MHC molecules and peptide requires formation of a complex between the 'ABC' peptide transporter, TAP, and newly synthesized class I molecules. Recent studies have provided new insights into the role of ATP in peptide binding, transport and release.
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Live-cell imaging has yielded surprising pictures of subcellular structures and dynamics in living plant cells. Recent studies illustrate the power of live-cell observation for revealing new biological phenomena and for generating new questions about plant cell structure and function.
Cloning of plant disease resistance genes is now commonplace in model plants. Recent attention has turned to how the proteins that they encode function biochemically to recognize their cognate Avirulence protein and to initiate the disease-resistance response. In addition, attention has turned to how the Avirulence proteins of pathogens might alter susceptible hosts for the benefit of the pathogen, and what plant proteins might be required for that process.
In the recent paper by Takaoka et al. (2003), the authors demonstrate that interferons-alpha and -beta stimulate p53 expression but not p53 activation. The increase in p53 expression translates into significant enhancement of apoptosis and reduction of chemotherapeutic dosages in vitro to destroy tumor cells. Furthermore, viral infections are also modulated by p53 in collaboration with interferons-alpha and -beta. These observations are significant and may lead to new paradigms for therapy if the high doses of interferon necessary to obtain the effects in vitro can be combined with more active interferons, interferons with minimal side effects, and/or novel delivery systems to target interferons directly to tumors.
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