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

We have developed a simple and highly efficient method to disrupt chromosomal genes in Escherichia coli in which PCR primers provide the homology to the targeted gene(s). In this procedure, recombination requires the phage lambda Red recombinase, which is synthesized under the control of an inducible promoter on an easily curable, low copy number plasmid. To demonstrate the utility of this approach, we generated PCR products by using primers with 36- to 50-nt extensions that are homologous to regions adjacent to the gene to be inactivated and template plasmids carrying antibiotic resistance genes that are flanked by FRT (FLP recognition target) sites. By using the respective PCR products, we made 13 different disruptions of chromosomal genes. Mutants of the arcB, cyaA, lacZYA, ompR-envZ, phnR, pstB, pstCA, pstS, pstSCAB-phoU, recA, and torSTRCAD genes or operons were isolated as antibiotic-resistant colonies after the introduction into bacteria carrying a Red expression plasmid of synthetic (PCR-generated) DNA. The resistance genes were then eliminated by using a helper plasmid encoding the FLP recombinase which is also easily curable. This procedure should be widely useful, especially in genome analysis of E. coli and other bacteria because the procedure can be done in wild-type cells.

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One-step inactivation of chromosomal genes in Escherichia coli K-12 using PCR products

The methods for detecting carcinogens and mutagens with the Salmonella mutagenicity test were described previously (Ames et al., 1975b). The present paper is a revision of the methods. Two new tester strains, a frameshift strain (TA97) and a strain carrying an ochre mutation on a multicopy plasmid (TA102), are added to the standard tester set. TA97 replaces TA1537. TA1535 and TA1538 are removed from the recommended set but can be retained at the option of the investigator. TA98 and TA100 are retained. We discuss other special purpose strains and present some minor changes in procedure, principally in the growth, storage, and preservation of the tester strains. Two substitutions are made in diagnostic mutagens to eliminate MNNG and 9-aminoacridine. Some test modifications are discussed.

Revised methods for the salmonella mutagenicity test

DNA Double-stranded Breaks Induce Histone H2AX Phosphorylation on Serine 139

Roles moleculaires des proteines de choc thermique dans le fonctionnement des organismes a des temperatures normales et suite a des chocs thermiques; differents genes impliques

The heat-shock proteins

UmuD2 Inhibits a Non-covalent Step during DinB-mediated Template Slippage on Homopolymeric Nucleotide Runs

Rhizobium meliloti exoD mutants are deficient in invasion of alfalfa nodules and, as a consequence, the nodules that exoD strains induce fail to fix nitrogen. These nodules appear to be arrested at the same stage as nodules induced by other exo mutants, which do not make an acidic exopolysaccharide called EPS I, or by ndv mutants, which do not produce a periplasmic cyclic beta(1,2) glucan. However previous genetic and biochemical evidence suggested that the nodule invasion defect of exoD mutants arose from a biochemical deficiency distinct from those of both EPS I-deficient exo mutants and ndv mutants. In this study, we characterize mutant phenotypes of exoD strains in both free-living and symbiotic states. Nodules induced by exoD mutants are generally small and empty of bacteria, and exhibit the same structural features as nodules induced by other invasion-deficient mutants. Putative incipient infection threads were visible in outer cortical cells of these nodules but not in the plant cells in the interior of the nodule. We show that exoD mutants are sensitive to alkaline conditions, ceasing to grow at elevated pH in liquid yeast extract cultures and exhibiting decreased viability in alkaline medium. Interestingly, we find that buffering the plant growth medium at slightly acidic pH (6.0-6.5) restores the ability of exoD mutants to invade alfalfa nodules. exoD mutants are thus alkali sensitive for both free-living and symbiotic phenotypes. This result implies that the nodule invasion defect of exoD mutants arises from their sensitivity to alkaline conditions and, furthermore, that alkaline conditions may obtain in the developing infection thread. The deduced amino acid sequence of ExoD is extremely hydrophobic, suggesting that the protein is membrane associated. We propose models whereby absence of a putative membrane protein might lead to sensitivity to alkaline conditions and consequent arrest of nodule invasion.

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Acidic conditions permit effective nodulation of alfalfa by invasion-deficient Rhizobium meliloti exoD mutants.

The mutH, mutL, mutS, and uvrD genes of Salmonella typhimurium LT2.

The ada gene of Escherichia coli K-12 encodes the regulatory protein for the adaptive response to alkylating agents. A set of plasmids carrying ordered deletions from the 3' end of the ada gene were isolated and characterized. These ada deletions encode fusion proteins that derive their amino termini from ada and their carboxyl termini from the downstream vector sequence that occurs before an in-frame stop codon. Several of these ada deletions encode Ada derivatives that constitutively activate ada transcription to very high levels. A second class of ada deletions encode Ada derivatives that are dominant inhibitors of the inducible transcription of ada but are inducible activators of alkA transcription. In addition, we found that two Ada derivatives containing the same ada sequences but fused to different vector-derived tails have strikingly different properties. One Ada derivative constitutively activates both ada and alkA expression to very high levels. In contrast, the other Ada derivative is an inducible activator of ada expression, like the wild-type Ada protein, but is not an inducible activator of alkA transcription. Our data suggest that the carboxyl terminus of the Ada protein plays a key role in modulating the ability of the Ada protein to function as a transcriptional activator.

Alteration of the carboxyl-terminal domain of Ada protein influences its inducibility, specificity, and strength as a transcriptional activator.

Cisplatin is a standard of care for lung cancer, yet platinum therapy rarely results in substantial tumor regression or a dramatic extension in patient survival. Here, we examined whether targeting Rev7 (also referred to as Mad2B, Mad2L2, and FANCV), a component of the translesion synthesis (TLS) machinery, could potentiate the action of cisplatin in non-small cell lung cancer (NSCLC) treatment. Rev7 loss led to an enhanced tumor cell sensitivity to cisplatin and dramatically improved chemotherapeutic response in a highly drug-resistant mouse model of NSCLC. While cisplatin monotherapy resulted in tumor cell apoptosis, Rev7 deletion promoted a cisplatin-induced senescence phenotype. Moreover, Rev7 deficiency promoted greater cisplatin sensitivity than that previously shown following targeting of other Pol ζ-proteins, suggesting that Pol ζ-dependent and -independent roles of Rev7 are relevant to cisplatin response. Thus, targeting Rev7 may represent a unique strategy for altering and enhancing chemotherapeutic response.

Graham C. Walker

Papers

UmuD2 Inhibits a Non-covalent Step during DinB-mediated Template Slippage on Homopolymeric Nucleotide Runs

Acidic conditions permit effective nodulation of alfalfa by invasion-deficient Rhizobium meliloti exoD mutants.

The mutH, mutL, mutS, and uvrD genes of Salmonella typhimurium LT2.

Alteration of the carboxyl-terminal domain of Ada protein influences its inducibility, specificity, and strength as a transcriptional activator.

Rev7 loss alters cisplatin response and increases drug efficacy in chemotherapy-resistant lung cancer.