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

umuD and umuC are essential genes for UV and most chemical mutagenesis in Escherichia coli (4, 15, 18) Both umuD and umuC mutants are virtually nonmutable with ultraviolet (UV) and a variety of chemicals (6, 17) The umuD and umuC genes are organized as an operon (4, 15) and encode proteins of 150 and 477 kilodaltons (kDa), respectively (7, 12) The umuDC operon is repressed by the LexA protein (1, 4) and regulated as a part of SOS response of E coli (10, 18, 19) SOS response occurs by activated RecA mediating the proteolytic cleavage of a bond between Ala84 and Gly85 of LexA (9), apparently facilitating a conditional autodigestion of LexA (16)

Antimutagenic Effect of umuD Mutant Plasmids: Isolation and Characterization of umuD Mutants Reduced in their Ability to Promote UV Mutagenesis in Escherichia Coli

Control and Function of Translesion DNA Polymerases

GUEST COMMENTARY Pseudo-B 12 Joins the Cofactor Family

properties of the encoded gene products. galactoglucan: genetic organization and meliloti directing the biosynthesis of The 32-kilobase exp gene cluster of Rhizobium

Graham C. Walker

Papers

Antimutagenic Effect of umuD Mutant Plasmids: Isolation and Characterization of umuD Mutants Reduced in their Ability to Promote UV Mutagenesis in Escherichia Coli

Control and Function of Translesion DNA Polymerases

GUEST COMMENTARY Pseudo-B 12 Joins the Cofactor Family

properties of the encoded gene products. galactoglucan: genetic organization and meliloti directing the biosynthesis of The 32-kilobase exp gene cluster of Rhizobium

LexA Regulatory System