Opposing roles of the holliday junction processing systems of Escherichia coli in recombination-dependent adaptive mutation

Aspects of the molecular mechanism of "adaptive" mutation are emerging from one experimental system: reversion of an Escherichia coli lac frameshift mutation carried on a conjugative plasmid. Homologous recombination is required and the mutations resemble polymerase errors. Reports implicating a role for conjugal transfer proteins suggested that the mutation mechanism is ordinary replication error occurring during transfer synthesis, followed by conjugation-like recombination, to capture the replicated fragment into an intact replicon. Whereas conjugational recombination uses either of two systems of Holliday junction resolution, we find that the adaptive lac reversions are inhibited by one resolution system and promoted by the other. Moreover, temporary absence of both resolution systems promotes mutation. These results imply that recombination intermediates themselves promote the mutations.     

Recombination and the progression of meiosis in Saccharomyces cerevisiae

Recombination is an essential part of meiosis: in almost all organisms, including Saccharomyces cerevisiae, proper chromosome segregation and the viability of meiotic products is dependent upon normal levels of recombination. In this article we examine the kinetics of the meiotic divisions in four mutants defective in the initiation of recombination. We find that mutations in any of three Early Exchange genes (REC104, REC114 or REC102) confer a phenotype in which the reductional division occurs earlier than in an isogenic wild-type diploid. We also present data confirming previous reports that strains with a mutation in the Early Exchange gene. MEI4 undergo the first division at about the same time as wild-type cells. The rec104 mutation is epistatic to the mei4 mutation for the timing of the first division. These observations suggest a possible relationship between the initiation of recombination and the timing of the reductional division. These data also allow these four Early Exchange genes examined to be distinguished in terms of their role in coordinating recombination with the reductional division.     

Recombination suppression by heterozygous Robertsonian chromosomes in the mouse

Robertsonian chromosomes are metacentric chromosomes formed by the joining of two telocentric chromosomes at their centromere ends. Many Robertsonian chromosomes of the mouse suppress genetic recombination near the centromere when heterozygous. We have analyzed genetic recombination and meiotic pairing in mice heterozygous for Robertsonian chromosomes and genetic markers to determine (1) the reason for this recombination suppression and (2) whether there are any consistent rules to predict which Robertsonian chromosomes will suppress recombination. Meiotic pairing was analyzed using synaptonemal complex preparations. Our data provide evidence that the underlying mechanism of recombination suppression is mechanical interference in meiotic pairing between Robertsonian chromosomes and their telocentric partners. The fact that recombination suppression is specific to individual Robertsonian chromosomes suggests that the pairing delay is caused by minor structural differences between the Robertsonian chromosomes and their telocentric homologs and that these differences arise during Robertsonian formation. Further understanding of this pairing delay is important for mouse mapping studies. In 10 mouse chromosomes (3, 4, 5, 6, 8, 9, 10, 11, 15 and 19) the distances from the centromeres to first markers may still be underestimated because they have been determined using only Robertsonian chromosomes. Our control linkage studies using C-band (heterochromatin) markers for the centromeric region provide improved estimates for the centromere-to-first-locus distance in mouse chromosomes 1, 2 and 16.     

Recombination in phage lambda: one geneticist's historical perspective

Several features of bacteriophage lambda suit it for the study of genetic recombination. Central among them are those that make it possible to correlate inheritance of DNA with the inheritance of information encoded by DNA through density-label equilibrium centrifugation. Such studies have revealed relationships between DNA replication and recombination, have identified roles for double-strand breaks in the initiation of recombination, and have elucidated the role of the recombination-stimulating sequence, chi.     

企业的联合重组与组织结构调整

从国际钢铁业联合重组，进行大规模兼并、收购和组成战略联盟发展趋势，分析了中国钢铁业如何面对组织结构调整带来的企业规模、研发效率和市场占有之争，并通过宝钢联合重组的案例，表明了国内钢铁企业走联合重组的道路是大有可为的。     

Recombination of protein domains facilitated by co-translational folding in eukaryotes

The evolution of complex genomes requires that new combinations of pre-existing protein domains successfully fold into modular polypeptides. During eukaryotic translation model two-domain polypeptides fold efficiently by sequential and co-translational folding of their domains. In contrast, folding of the same proteins in Escherichia coli is posttranslational, and leads to intramolecular misfolding of concurrently folding domains. Sequential domain folding in eukaryotes may have been critical in the evolution of modular polypeptides, by increasing the probability that random gene-fusion events resulted in immediately foldable protein structures.     

Recombination of engineered defective RNA species produces infective potyvirus in planta

Recombination occurred between viral genomes when squash plants were cobombarded with mixtures of engineered disabled constructs of a zucchini yellow mosaic potyvirus. Single and double recombinants were detected in the progeny. Genes involved in the recombination process and the mechanisms of recombination were studied in potyviruses for the first time.     

债务重组的财务策略和财务监督

分析了债务重组的原因 ,指出财务策略应着重于选择债务重组方式、确定债务重组日、规定好附加条件、确定非现金资产价格 ,在债务重组时应建立相应的约束、监督机制 ,进行有效监督 ,避免国有资产流失     

江西稀土产业的重组与战略

在全面阐述与分析我国和江西稀土产业发展现状的基础上，依据产业经济、战略管理、企业组织、管理学及公司治理等有关学科和理论，运用战略管理的SWOT分析、价值链分析、动态分析和比较分析相结合的方法，探讨江西稀土产业结构调整和企业重组，实现集约化经营，提高产业核心竞争力的发展战略，对组建稀土集团所涉及的股权设置、公司治理结构、组织结构设计、管理模式等进行了有益的探索，为江西省稀土产业的调整和未来发展战略，适应新的国际竞争环境提供一定的参考。     

试论冶金企业物流系统的重组

对物流在企业发展中的重要意义以及物流重组过程中存在的问题及解决方案进行了探讨。     

Recombination in Tula hantavirus evolution: analysis of genetic lineages from Slovakia

To examine the evolution of Tula hantavirus (TUL), carried by the European common vole (Microtus arvalis and M. rossiaemeridionalis), we have analyzed genetic variants from Slovakia, the country where the virus is endemic. Phylogenetic analysis (PHYLIP) based on either partial (nucleotides [nt] 441 to 898) or complete N-protein-encoding sequences divided Slovakian TUL variants into two main lineages: (i) strains from eastern Slovakia, which clustered with Russian strains, and (ii) strains from western Slovakia situated closer to those from the Czech Republic. We found genetic diversity of 19% between the two groups and 4% within the western Slovakian TUL strains. Phylogenetic analysis of the 3' noncoding region (3'-NCR), however, placed the eastern Slovakian strains closer to those from western Slovakia and the Czech Republic, with a greater distance to the Russian strains, suggesting a recombinant nature of the S segment in the eastern Slovakian TUL lineage. A bootscan search of the S-segment sequences of TUL strains revealed at least two recombination points in the S sequences of eastern Slovakian TUL strains (nt 400 to 415 and around 1200) which agreed well with the pattern of amino acid substitutions in the N protein and deletions/insertions in the 3'-NCR of the S segment. These data suggest that homologous recombination events occurred in the evolution of hantaviruses.