南海北部地壳结构的深地震探测和研究新进展

南海是西太平洋最大的边缘海之一,其北部具有被动大陆边缘特征.深部地壳结构的研究对深入认识南海北部边缘的构造属性、演化历史、含油气盆地的形成过程,以及南海成因具有十分重要的意义.南海北部地壳结构的深地震探测经历了声纳浮标、双船扩展剖面和海底地震仪几个阶段,声纳浮标探测了解到上地壳的结构特征,双船扩展剖面首次获得了地壳结构和莫霍面起伏的情况,海底地震仪探测则得到了详细的地壳结构模型.文中回顾了这些深地震探测和研究的历史,介绍和总结了最新的研究进展和重要成果,并提出存在的问题和今后工作的建议.     

The roads from phenotypic variation to gene discovery: mutagenesis versus QTLs

In model organisms, chemical mutagenesis provides a powerful alternative to natural, polygenic variation (for example, quantitative trait loci (QTLs)) for identifying functional pathways and complex disease genes. Despite recent progress in QTLs, we expect that mutagenesis is will ultimately prove more effective because the prospects of gene identification are high and every gene affecting a trait is potentially a target.     

ATM phosphorylates p95/nbs1 in an S-phase checkpoint pathway

The rare diseases ataxia-telangiectasia (AT), caused by mutations in the ATM gene, and Nijmegen breakage syndrome (NBS), with mutations in the p95/nbs1 gene, share a variety of phenotypic abnormalities such as chromosomal instability, radiation sensitivity and defects in cell-cycle checkpoints in response to ionizing radiation. The ATM gene encodes a protein kinase that is activated by ionizing radiation or radiomimetic drugs, whereas p95/nbs1 is part of a protein complex that is involved in responses to DNA double-strand breaks. Here, because of the similarities between AT and NBS, we evaluated the functional interactions between ATM and p95/nbs1. Activation of the ATM kinase by ionizing radiation and induction of ATM-dependent responses in NBS cells indicated that p95/nbs1 may not be required for signalling to ATM after ionizing radiation. However, p95/nbs1 was phosphorylated on serine 343 in an ATM-dependent manner in vitro and in vivo after ionizing radiation. A p95/nbs1 construct mutated at the ATM phosphorylation site abrogated an S-phase checkpoint induced by ionizing radiation in normal cells and failed to compensate for this functional deficiency in NBS cells. These observations link ATM and p95/nbs1 in a common signalling pathway and provide an explanation for phenotypic similarities in these two diseases.     

Superconductivity in molecular crystals induced by charge injection

Progress in the field of superconductivity is often linked to the discovery of new classes of materials, with the layered copper oxides being a particularly impressive example. The superconductors known today include a wide spectrum of materials, ranging in complexity from simple elemental metals, to alloys and binary compounds of metals, to multi-component compounds of metals and chalcogens or metalloids, doped fullerenes and organic charge-transfer salts. Here we present a new class of superconductors: insulating organic molecular crystals that are made metallic through charge injection. The first examples are pentacene, tetracene and anthracene, the last having the highest transition temperature, at 4 K. We anticipate that many other organic molecular crystals can also be made superconducting by this method, which will lead to surprising findings in the vast composition space of molecular crystals.     

Helical self-assembled polymers from cooperative stacking of hydrogen-bonded pairs

The double helix of DNA epitomizes this molecule's ability to self-assemble in aqueous solutions into a complex chiral structure using hydrogen bonding and hydrophobic interactions. Non-covalently interacting molecules in organic solvents are used to design systems that similarly form controlled architectures. Peripheral chiral centres in assemblies and chiral side chains attached to a polymer backbone, have been shown to induce chirality at the supramolecular level, and highly ordered structures stable in water are also known. However, it remains difficult to rationally exploit non-covalent interactions for the formation of chiral assemblies that are stable in water, where solvent molecules can compete effectively for hydrogen bonds. Here we describe a general strategy for the design of functionalized monomer units and their association in either water or alkanes into non-covalently linked polymeric structures with controlled helicity and chain length. The monomers consist of bifunctionalized ureidotriazine units connected by a spacer and carrying solubilizing chains at the periphery. This design allows for dimerization through self-complementary quadruple hydrogen bonding between the units and solvophobically induced stacking of the dimers into columnar polymeric architectures, whose structure and helicity can be adjusted by tuning the nature of the solubilizing side chains.     

The crystal structure of DNA mismatch repair protein MutS binding to a G x T mismatch

DNA mismatch repair ensures genomic integrity on DNA replication. Recognition of a DNA mismatch by a dimeric MutS protein initiates a cascade of reactions and results in repair of the newly synthesized strand; however, details of the molecular mechanism remain controversial. Here we present the crystal structure at 2.2 A of MutS from Escherichia coli bound to a G x T mismatch. The two MutS monomers have different conformations and form a heterodimer at the structural level. Only one monomer recognizes the mismatch specifically and has ADP bound. Mismatch recognition occurs by extensive minor groove interactions causing unusual base pairing and kinking of the DNA. Nonspecific major groove DNA-binding domains from both monomers embrace the DNA in a clamp-like structure. The interleaved nucleotide-binding sites are located far from the DNA. Mutations in human MutS alpha (MSH2/MSH6) that lead to hereditary predisposition for cancer, such as hereditary non-polyposis colorectal cancer, can be mapped to this crystal structure.     

The mouse Dreher gene Lmx1a controls formation of the roof plate in the vertebrate CNS

In the vertebrate central nervous system (CNS), a cascade of signals that originates in the ectoderm adjacent to the neural tube is propagated by the roof plate to dorsalize the neural tube. Here we report that the phenotype of the spontaneous neurological mutant mouse dreher (dr) results from a failure of the roof plate to develop. Dorsalization of the neural tube is consequently affected: dorsal interneurons in the spinal cord and granule neurons in the cerebellar cortex are lost, and the dorsal vertebral neural arches fail to form. Positional cloning of dreher indicates that the LIM homeodomain protein, Lmx1a, is affected in three different alleles of dreher. Lmx1a is expressed in the roof plate along the neuraxis during development of the CNS. Thus, Lmx1a is required for development of the roof plate and, in turn, for specification of dorsal cell fates in the CNS and developing vertebrae.