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Orientation specificity of the Lactococcus lactis Chi site
Author(s) -
El Karoui Meriem,
Schaeffer Matthieu,
Biaudet Véronique,
Bolotin Alexandre,
Sorokin Alexeï,
Gruss Alexandra
Publication year - 2000
Publication title -
genes to cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.912
H-Index - 115
eISSN - 1365-2443
pISSN - 1356-9597
DOI - 10.1046/j.1365-2443.2000.00342.x
Subject(s) - recbcd , biology , lactococcus lactis , homologous recombination , helicase , exonuclease , genetics , genome , dna , dna replication , dna repair , bacteria , gene , lactic acid , rna , dna polymerase
Background In Escherichia coli , the Chi sequence modulates the activity of RecBCD, a powerful double‐stranded (ds) DNA exonuclease/helicase. Chi attenuates RecBCD exonuclease activity and stimulates homologous recombination in an orientation‐dependent manner. Chi Ec is frequent and over‐represented on its genome, which is thought to be related to its role in dsDNA break repair. We previously identified a Chi‐like sequence (referred to as Chi Ll ) and an exonuclease/helicase in the Gram‐positive bacterium Lactococcus lactis . Chi Ll and RexAB are functional analogues of Chi Ec and RecBCD. Results We report that Chi Ll attenuates RexAB exonuclease activity and stimulates homologous recombination in an orientation‐dependent manner. Analysis of Chi Ll distribution on the L. lactis chromosome reveals that Chi Ll is frequent, highly over‐represented, and oriented with respect to the direction of replication. Conclusion Our results show that a single orientation of Chi Ll interacts with RexAB. The active orientation is preferentially found on the replication leading strand of the L. lactis genome, consistent with a primary role of Chi Ll in repair of dsDNA breaks at the replication fork. We propose that orientation‐dependence of Chi activity and over‐representation of Chi sequences on bacterial genomes may be conserved properties of exonuclease/helicase–Chi couples. Other properties of the Chi sequence distribution on the genomes might reflect more specific characteristics of each couple and of the host.