The initiation and control of homologous recombination in escherichia coli

1995 ◽  
Vol 347 (1319) ◽  
pp. 13-20 ◽  
Keyword(s):  
Escherichia Coli ◽  
Low Frequency ◽  
Nuclease Activity ◽  
X Rays ◽  
Single Stranded Dna ◽  
Dna Break ◽  
Dna Break Repair ◽  
Break Repair ◽  
Recbcd Enzyme ◽  
Dna Ends

The chromosome of Escherichia coli recombines at low frequency when it is an intact circle but recombines at high frequency when it is broken, for example by X-rays, or when a linear DNA fragment is introduced into the cell during conjugation or transduction. The high recombinogenicity of double-strand (ds) DNA ends is attributable to RecBCD enzyme, which acts on ds DNA ends and is essential for recombination and ds DNA break repair. RecBCD enzyme initiates DNA unwinding at ds DNA ends, and its nuclease activity is controlled by Chi sites (5' G-C-T-G-G-T-G-G 3') in such a way that the enzyme produces a potent single-stranded DNA substrate for homologous pairing by RecA and single-stranded DNA binding proteins. We discuss a unifying model for recombination and ds DNA break repair, based upon the enzymic activities of these and other proteins and upon the behaviour of E. coli mutants altered in these proteins.

scholarly journals Effects of recJ, recQ, and recFOR Mutations on Recombination in Nuclease-Deficient recB recD Double Mutants of Escherichia coli

2005 ◽  
Vol 187 (4) ◽  
pp. 1350-1356 ◽  
Author(s):  
Ivana Ivančić-Baće ◽  
Erika Salaj-Šmic ◽  
Krunoslav Brčić-Kostić
Keyword(s):  
Escherichia Coli ◽  
Double Mutant ◽  
Reca Protein ◽  
Recq Helicase ◽  
Single Stranded Dna ◽  
Double Stranded Dna ◽  
Recf Pathway ◽  
Recombination Pathway ◽  
Recbcd Enzyme ◽  
Dna Ends

ABSTRACT The two main recombination pathways in Escherichia coli (RecBCD and RecF) have different recombination machineries that act independently in the initiation of recombination. Three essential enzymatic activities are required for early recombinational processing of double-stranded DNA ends and breaks: a helicase, a 5′→3′ exonuclease, and loading of RecA protein onto single-stranded DNA tails. The RecBCD enzyme performs all of these activities, whereas the recombination machinery of the RecF pathway consists of RecQ (helicase), RecJ (5′→3′ exonuclease), and RecFOR (RecA-single-stranded DNA filament formation). The recombination pathway operating in recB (nuclease-deficient) mutants is a hybrid because it includes elements of both the RecBCD and RecF recombination machineries. In this study, genetic analysis of recombination in a recB (nuclease-deficient) recD double mutant was performed. We show that conjugational recombination and DNA repair after UV and gamma irradiation in this mutant are highly dependent on recJ, partially dependent on recFOR, and independent of recQ. These results suggest that the recombination pathway operating in a nuclease-deficient recB recD double mutant is also a hybrid. We propose that the helicase and RecA loading activities belong to the RecBCD recombination machinery, while the RecJ-mediated 5′→3′ exonuclease is an element of the RecF recombination machinery.

RecFOR Function Is Required for DNA Repair and Recombination in a RecA Loading-Deficient recB Mutant of Escherichia coli

Genetics ◽  
2003 ◽  
Vol 163 (2) ◽  
pp. 485-494 ◽  
Author(s):  
Ivana Ivančić-Baće ◽  
Petra Peharec ◽  
Sunčana Moslavac ◽  
Nikolina Škrobot ◽  
Erika Salaj-Šmic† ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Reca Protein ◽  
Nuclease Activity ◽  
Filament Formation ◽  
Single Stranded Dna ◽  
Catalytic Center ◽  
In Vivo Assays ◽  
Recbcd Enzyme ◽  
Contradictory Data

Abstract The RecA loading activity of the RecBCD enzyme, together with its helicase and 5′ → 3′ exonuclease activities, is essential for recombination in Escherichia coli. One particular mutant in the nuclease catalytic center of RecB, i.e., recB1080, produces an enzyme that does not have nuclease activity and is unable to load RecA protein onto single-stranded DNA. There are, however, previously published contradictory data on the recombination proficiency of this mutant. In a recF– background the recB1080 mutant is recombination deficient, whereas in a recF+ genetic background it is recombination proficient. A possible explanation for these contrasting phenotypes may be that the RecFOR system promotes RecA-single-strand DNA filament formation and replaces the RecA loading defect of the RecB1080CD enzyme. We tested this hypothesis by using three in vivo assays. We compared the recombination proficiencies of recB1080, recO, recR, and recF single mutants and recB1080 recO, recB1080 recR, and recB1080 recF double mutants. We show that RecFOR functions rescue the repair and recombination deficiency of the recB1080 mutant and that RecA loading is independent of RecFOR in the recB1080 recD double mutant where this activity is provided by the RecB1080C(D–) enzyme. According to our results as well as previous data, three essential activities for the initiation of recombination in the recB1080 mutant are provided by different proteins, i.e., helicase activity by RecB1080CD, 5′ → 3′ exonuclease by RecJ- and RecA-single-stranded DNA filament formation by RecFOR.

A Domain of RecC Required for Assembly of the Regulatory RecD Subunit Into the Escherichia coli RecBCD Holoenzyme

Genetics ◽  
2002 ◽  
Vol 161 (2) ◽  
pp. 483-492
Author(s):  
Susan K Amundsen ◽  
Andrew F Taylor ◽  
Gerald R Smith
Keyword(s):  
Escherichia Coli ◽  
Nuclease Activity ◽  
Activity Analysis ◽  
Interaction Domain ◽  
Major Pathway ◽  
Deletion Mutations ◽  
High Affinity ◽  
C Terminus ◽  
Recbcd Enzyme ◽  
Dna Ends

Abstract The heterotrimeric RecBCD enzyme of Escherichia coli is required for the major pathway of double-strand DNA break repair and genetic exchange. Assembled as a heterotrimer, the enzyme has potent nuclease and helicase activity. Analysis of recC nonsense and deletion mutations revealed that the C terminus of RecC is required for assembly of the RecD subunit into RecBCD holoenzyme but not for recombination proficiency; the phenotype of these mutations mimics that of recD deletion mutations. Partial proteolysis of purified RecC polypeptide yielded a C-terminal fragment that corresponds to the RecD-interaction domain. RecD is essential for nuclease activity, regulation by the recombination hotspot Chi, and high affinity for DNA ends. The RecC-RecD interface thus appears critical for the regulation of RecBCD enzyme via the assembly and, we propose, disassembly or conformational change of the RecD subunit.

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