抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

https://njc.rockefeller.edu/pdf4/Class2-LeeAmbros1993.pdf

The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14

We have developed a new vector strategy for the insertion of foreign genes into the genomes of gram negative bacteria not closely related to Escherichia coli. The system consists of two components: special E. coli donor strains and derivatives of E. coli vector plasmids. The donor strains (called mobilizing strains) carry the transfer genes of the broad host range IncP–type plasmid RP4 integrated in their chromosomes. They can utilize any gram negative bacterium as a recipient for conjugative DNA transfer. The vector plasmids contain the P–type specific recognition site for mobilization (Mob site) and can be mobilized with high frequency from the donor strains. The mobilizable vectors are derived from the commonly used E. coli vectors pACYC184, pACYC177, and pBR325, and are unable to replicate in strains outside the enteric bacterial group. Therefore, they are widely applicable as transposon carrier replicons for random transposon insertion mutagenesis in any strain into which they can be mobilized but not stably maintained. The vectors are especially useful for site–directed transposon mutagenesis and for site–specific gene transfer in a wide variety of gram negative organisms.

A broad host range mobilization system for in vivo genetic engineering: transposon mutagenesis in Gram negative bacteria

We describe Hi-C, a method that probes the three-dimensional architecture of whole genomes by coupling proximity-based ligation with massively parallel sequencing. We constructed spatial proximity maps of the human genome with Hi-C at a resolution of 1 megabase. These maps confirm the presence of chromosome territories and the spatial proximity of small, gene-rich chromosomes. We identified an additional level of genome organization that is characterized by the spatial segregation of open and closed chromatin to form two genome-wide compartments. At the megabase scale, the chromatin conformation is consistent with a fractal globule, a knot-free, polymer conformation that enables maximally dense packing while preserving the ability to easily fold and unfold any genomic locus. The fractal globule is distinct from the more commonly used globular equilibrium model. Our results demonstrate the power of Hi-C to map the dynamic conformations of whole genomes.

/pdf/comprehensive-mapping-of-long-range-interactions-reveals-15wp5ww9ic.pdf

Comprehensive mapping of long-range interactions reveals folding principles of the human genome.

Use of bacteriophage T7 RNA polymerase to direct selective high-level expression of cloned genes

Interactions between and along chromosomes during meiosis

All of the DNA cleavage and strand transfer events required for transposition of insertion sequence IS10 are carried out by a 46-kDa IS10-encoded transposase protein. Limited proteolysis demonstrates that transposase has two principal structural domains, a 28-kDa N-terminal domain (N alpha beta; aa 1-246) and a 17-kDa C-terminal domain (C; aa 256-402). The two domains are connected by a 1-kDa proteolytic-sensitive linker region (aa 247-255). The N-terminal domain N alpha beta can be further subdivided into domains N alpha and N beta by a weaker protease-sensitive site located 6 kDa (53 aa) from the N terminus. The N beta and N alpha beta fragments are capable of nonspecific DNA binding as determined by Southwestern blot analysis. None of the fragments alone is capable of carrying out the first step of transposition, assembly of a synaptic complex containing a pair of transposon ends. Remarkably, complete transposition activity can be reconstituted by mixing fragment N alpha beta and fragment C, with or without the intervening linker region. We infer that the structural integrity of transposase during the transitions involved in the chemical steps of the transposition reaction is maintained independent of the linker, presumably by direct contacts between and among the principal domains. Reconstitution of activity in the absence of the linker region is puzzling, however, because mutations that block strand transfer or affect insertion specificity alter linker region residues. Additional reconstitution experiments demonstrate that the N alpha region is dispensable for formation of a synaptic complex but is required for complexes to undergo cleavage.

Structural domains of IS10 transposase and reconstitution of transposition activity from proteolytic fragments lacking an interdomain linker

Meiotic chromosome dynamics

We have described three illegitimate recombination events associated with, but not promoted by, transposon Tn10: precise excision, nearly precise excision, and precise excision of a nearly precise excision remnant. All three are structurally analogous: excision occurs between two short direct repeat sequences, removing all intervening material plus one copy of the direct repeat. In each case, the direct repeats border a larger inverted repeat. We report here the isolation of host mutants of Escherichia coli K12 which exhibit increased frequencies of precise excision of Tn10. Nineteen of the 39 mutants have been mapped to five distinct loci on the E. coli genetic map and have been designated texA through texE (for Tn10 excision). Mapping and genetic characterization indicate that each tex gene corresponds to a previously identified gene involved in cellular DNA metabolism: recB and/or recC, uvrD, mutH, mutS, and dam. The role of these various DNA repair and recombination genes in an illegitimate recombination process such as Tn10 excision will be discussed. In addition to an increase in precise excision frequency, all 39 tex mutants display an increased frequency for nearly precise excision. However, none of the mutants are increased for the third excision event, precise excision of a nearly precise excision remnant, supporting the idea that precise and nearly precise excision occur by closely related pathways which are distinct from those pathways which promote the third type of excision event.

Mutants of Escherichia coli K12 which affect excision of transposon Tn10.

In Saccharomyces cerevisiae, the RAD50 gene is required for repair of X-ray and MMS-induced DNA damage during vegetative growth, and for synaptonemal complex formation and genetic recombination during meiosis We show below that the RAD50 gene encodes major and minor transcripts of 42 and 46 kb in length which differ primarily at their 5′ ends Steady-state levels of both RAD50 transcripts increase coordinately during meiosis, reaching maximal levels midway through meiotic prophase, about 3 or 4 h after transfer of cells to sporulation medium The 5′ ends of the major RAD50 transcript in both meiotic and vegetative cells map to the same cluster of sites approximately 20 by upstream of the amino-terminal ATG of the RAD50 coding sequence We conclude that the increased RAD50 transcript level observed during meiosis does not reflect utilization of a new promoter In contrast, steady-state levels of Rad50 protein do not increase during meiosis Thus, changes in RAD50 transcript levels are not neccessarily accompanied by commensurate changes in Rad50 protein levels Possible explanations are considered

/pdf/expression-of-the-saccharomyces-cerevisiae-rad50-gene-during-1b7albcpk3.pdf

Expression of the Saccharomyces cerevisiae RAD50 gene during meiosis: steady-state transcript levels rise and fall while steady-state protein levels remain constant

Nancy Kleckner

Papers

Interactions between and along chromosomes during meiosis

Structural domains of IS10 transposase and reconstitution of transposition activity from proteolytic fragments lacking an interdomain linker

Meiotic chromosome dynamics

Mutants of Escherichia coli K12 which affect excision of transposon Tn10.

Expression of the Saccharomyces cerevisiae RAD50 gene during meiosis: steady-state transcript levels rise and fall while steady-state protein levels remain constant