XthA (Exonuclease III) regulates loading of RecA onto DNA substrates in log phase Escherichia coli cells. 2008

Richard C Centore, and Roxane Lestini, and Steven J Sandler
Molecular and Cellular Biology Graduate Program, Morrill Science Center, University of Massachusetts at Amherst, Amherst, MA 01003, USA.

Exonucleases can modify DNA substrates created during DNA replication, recombination and repair. In Escherichia coli, the effects of several 3'-5' exonucleases on RecA loading were studied by assaying RecA-GFP foci formation. Mutations in xthA (ExoIII), xseAB (ExoVII), xni (ExoIX), exoX (ExoX) and tatD (ExoXI) increased the number of RecA-GFP foci twofold to threefold in a population of log phase cells grown in minimal medium. These increases depend on xonA. Epistasis analysis shows that ExoVII, ExoX, ExoIX and ExoXI function in a common pathway, distinct from ExoIII (and ExoI is upstream of both pathways). It is shown (paradoxically) that in xthA mutants, RecA-GFP loading is predominantly RecBCD-dependent and that xthA recB double mutants are viable. Experiments show that while log phase xthA cells have twofold more double-stranded breaks (DSBs) than wild type, they do not induce the SOS response. The increase in RecA loading is independent of the base excision repair (BER) proteins Nth, MutM and Nei. It is proposed that log phase cells produce DSBs that do not induce the SOS response. Furthermore, ExoI, ExoIII and the other 3'-5' exonucleases process these DSBs, antagonizing the RecBCD pathway of RecA loading, thus regulating the availability of these substrates for recombination.

UI MeSH Term Description Entries
D011938 Rec A Recombinases A family of recombinases initially identified in BACTERIA. They catalyze the ATP-driven exchange of DNA strands in GENETIC RECOMBINATION. The product of the reaction consists of a duplex and a displaced single-stranded loop, which has the shape of the letter D and is therefore called a D-loop structure. Rec A Protein,RecA Protein,Recombinases, Rec A
D011993 Recombinant Fusion Proteins Recombinant proteins produced by the GENETIC TRANSLATION of fused genes formed by the combination of NUCLEIC ACID REGULATORY SEQUENCES of one or more genes with the protein coding sequences of one or more genes. Fusion Proteins, Recombinant,Recombinant Chimeric Protein,Recombinant Fusion Protein,Recombinant Hybrid Protein,Chimeric Proteins, Recombinant,Hybrid Proteins, Recombinant,Recombinant Chimeric Proteins,Recombinant Hybrid Proteins,Chimeric Protein, Recombinant,Fusion Protein, Recombinant,Hybrid Protein, Recombinant,Protein, Recombinant Chimeric,Protein, Recombinant Fusion,Protein, Recombinant Hybrid,Proteins, Recombinant Chimeric,Proteins, Recombinant Fusion,Proteins, Recombinant Hybrid
D004260 DNA Repair The removal of DNA LESIONS and/or restoration of intact DNA strands without BASE PAIR MISMATCHES, intrastrand or interstrand crosslinks, or discontinuities in the DNA sugar-phosphate backbones. DNA Damage Response
D004269 DNA, Bacterial Deoxyribonucleic acid that makes up the genetic material of bacteria. Bacterial DNA
D004843 Epistasis, Genetic A form of gene interaction whereby the expression of one gene interferes with or masks the expression of a different gene or genes. Genes whose expression interferes with or masks the effects of other genes are said to be epistatic to the effected genes. Genes whose expression is affected (blocked or masked) are hypostatic to the interfering genes. Deviation, Epistatic,Epistatic Deviation,Genes, Epistatic,Genes, Hypostatic,Epistases, Genetic,Gene-Gene Interaction, Epistatic,Gene-Gene Interactions, Epistatic,Genetic Epistases,Genetic Epistasis,Interaction Deviation,Non-Allelic Gene Interactions,Epistatic Gene,Epistatic Gene-Gene Interaction,Epistatic Gene-Gene Interactions,Epistatic Genes,Gene Gene Interaction, Epistatic,Gene Gene Interactions, Epistatic,Gene Interaction, Non-Allelic,Gene Interactions, Non-Allelic,Gene, Epistatic,Gene, Hypostatic,Hypostatic Gene,Hypostatic Genes,Interaction, Epistatic Gene-Gene,Interaction, Non-Allelic Gene,Interactions, Epistatic Gene-Gene,Interactions, Non-Allelic Gene,Non Allelic Gene Interactions,Non-Allelic Gene Interaction
D005090 Exodeoxyribonucleases A family of enzymes that catalyze the exonucleolytic cleavage of DNA. It includes members of the class EC 3.1.11 that produce 5'-phosphomonoesters as cleavage products. DNA Exonucleases,Exonucleases, DNA
D013014 SOS Response, Genetics An error-prone mechanism or set of functions for repairing damaged microbial DNA. SOS functions (a concept reputedly derived from the SOS of the international distress signal) are involved in DNA repair and mutagenesis, in cell division inhibition, in recovery of normal physiological conditions after DNA repair, and possibly in cell death when DNA damage is extensive. SOS Response (Genetics),SOS Box,SOS Function,SOS Induction,SOS Region,SOS Repair,SOS Response,SOS System,Box, SOS,Function, SOS,Functions, SOS,Genetics SOS Response,Genetics SOS Responses,Induction, SOS,Inductions, SOS,Region, SOS,Regions, SOS,Repair, SOS,Repairs, SOS,Response, Genetics SOS,Response, SOS,Response, SOS (Genetics),Responses, Genetics SOS,Responses, SOS,Responses, SOS (Genetics),SOS Functions,SOS Inductions,SOS Regions,SOS Repairs,SOS Responses,SOS Responses (Genetics),SOS Responses, Genetics,SOS Systems,System, SOS,Systems, SOS
D048168 Escherichia coli K12 A species of gram-negative, rod-shaped bacteria belonging to the K serogroup of ESCHERICHIA COLI. It lives as a harmless inhabitant of the human LARGE INTESTINE and is widely used in medical and GENETIC RESEARCH. E coli K12
D049452 Green Fluorescent Proteins Protein analogs and derivatives of the Aequorea victoria green fluorescent protein that emit light (FLUORESCENCE) when excited with ULTRAVIOLET RAYS. They are used in REPORTER GENES in doing GENETIC TECHNIQUES. Numerous mutants have been made to emit other colors or be sensitive to pH. Green Fluorescent Protein,Green-Fluorescent Protein,Green-Fluorescent Proteins,Fluorescent Protein, Green,Fluorescent Proteins, Green,Protein, Green Fluorescent,Protein, Green-Fluorescent,Proteins, Green Fluorescent,Proteins, Green-Fluorescent
D050296 Microbial Viability Ability of a microbe to survive under given conditions. This can also be related to a colony's ability to replicate. Bacterial Viability,Virus Viability,Bacteria Viability,Microbial Inactivation,Inactivation, Microbial,Viability, Bacteria,Viability, Bacterial,Viability, Microbial,Viability, Virus

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