Effect of Host Species on RecG Phenotypes in Helicobacter pylori and Escherichia coli

Abstract

Recombination is a fundamental mechanism for the generation of genetic variation. Helicobacter pylori strains have different frequencies of intragenomic recombination, arising from deletions and duplications between DNA repeat sequences, as well as intergenomic recombination, facilitated by their natural competence. We identified a gene, hp1523, that influences recombination frequencies in this highly diverse bacterium and demonstrate its importance in maintaining genomic integrity by limiting recombination events. HP1523 shows homology to RecG, an ATP-dependent helicase that in Escherichia coli allows repair of damaged replication forks to proceed without recourse to potentially mutagenic recombination. Cross-species studies done show that hp1523 can complement E. coli recG mutants in trans to the same extent as E. coli recG can, indicating that hp1523 has recG function. The E. coli recG gene only partially complements the hp1523 mutation in H. pylori. Unlike other recG homologs, hp1523 is not involved in DNA repair in H. pylori, although it has the ability to repair DNA when expressed in E. coli. Therefore, host context appears critical in defining the function of recG. The fact that in E. coli recG phenotypes are not constant in other species indicates the diverse roles for conserved recombination genes in prokaryotic evolution.

Structural and Functional Divergence of MutS2 from Bacterial MutS1 and Eukaryotic MSH4-MSH5 Homologs

“…Inverse PCR using primers MutinvF1 and MutinvR1 (Table 2) created BamHI restriction sites, and the aphA cassette, conferring kanamycin resistance (Km r ), was used to interrupt the open reading frame (ORF) to create pMutS2Km. Since it is not involved in recombination, the vacA locus (HP0887) was chosen as a control for the presence of the aphA cassette (8,33). The recA locus (HP0153) was interrupted as another control, since several phenotypes related to this study have been characterized (7,67).…”

“…The recA locus (HP0153) was interrupted as another control, since several phenotypes related to this study have been characterized (7,67). pVacAKm and pRecAKm, as previously constructed (33), were used to transform HP strain JP26, as described previously (71), to create JP26 vacA::aphA and JP26 recA::aphA. Strain JP26 also was transformed to Km r with pMutS2Km to create JP26 mutS2::aphA.…”

“…Strain JP26 also was transformed to Km r with pMutS2Km to create JP26 mutS2::aphA. Chromosomal DNA was isolated from the putative mutant strains, and the correct insertion of the aphA cassette into the expected ORF was confirmed by PCR in each case, as described previously (33).…”

A Recombination Puzzle Solved: Role for New DNA Repair Systems in Helicobacter pylori Diversity/Persistence

“…In E. coli, an alternative pathway processing branch migration of Holliday junctions is the RecG helicase. In marked contrast to E. coli, H. pylori recG mutants do not have defective DNA repair, as measured by UV-light sensitivity and ciprofloxacin susceptibility [76]. Furthermore, H. pylori recG mutants have increased frequencies of intergenomic recombination and deletion, suggesting that branch migration and Holliday junction resolution are more efficient in the absence of RecG function [75,76].…”

Change Is Good: Variations in Common Biological Mechanisms in the Epsilonproteobacterial GeneraCampylobacterandHelicobacter

“…This phenomenon is likely due to the absence of the resolvase enzyme, RusA, that is usually associated with the RecG recombination pathway (308). Interestingly, H. pylori RecG is able to complement an E. coli recG mutant to the same extent as E. coli RecG (310). Thus, the species-specific antirepair function of the H. pylori RecG helicase may provide a means to maintain genetic diversity within a population of cells while still preserving crit- 98 GILBREATH ET AL.…”