title: Chi-star, a chi-related 11-mer sequence partially active in an E. coli recC1004 strain.
abstract: BACKGROUND
  chi sequence (5'GCTGGTGG) of Escherichia coli was first identified as a site that increased the plaque size of bacteriophage lambda. Subsequent studies showed that this site is responsible for both the attenuation ofRecBCD exonuclease activity and the promotion of RecA, RecBCD-mediated recombination. It is known that bacteriophage lambda containing the chi site makes very small plaques on a recC* (recC1004) mutant because chi is not recognized by the RecBC*D mutant enzyme.
  
  
  RESULTS
  We cloned E. coli chromosomal fragments in lambda which allowed lambda to form larger plaques on this recC1004 mutant. The fragments were found to share a chi-like 11-mer sequence, 5'GCTGGTGCTCG. Substitution of these fragments with a synthetic 11-mer of this sequence and single-base-pair substitution analysis of its last four nucleotides demonstrated that this sequence is both necessary and sufficient for the observed activity. The sequence, designated X* (chi-star), protected rolling-circle DNA replication in the recC1004 mutant and in the recBCD+ strain, most likely because it attenuated the exonuclease activity of the RecBC*D and RecBCD+ enzyme. chi-star, did not significantly stimulate lambda recombination in two assays.
  
  
  CONCLUSIONS
  We have discovered that a mutant RecBCD enzyme responds, in vivo, to a longer chi variant.
authors.affiliation: Department of Molecular Biology, Institute of Medical Science, University of Tokyo, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Handa
authors.forename: S
authors.initials: S
authors.lastname: Ohashi
authors.forename: K
authors.initials: K
authors.lastname: Kusano
authors.forename: I
authors.initials: I
authors.lastname: Kobayashi
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics; D003001:Cloning, Molecular; D004261:DNA Replication; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000235:genetics*; D009154:Mutation; D010957:Plasmids; D011995:Recombination, Genetic
chemical_list: D029968:Escherichia coli Proteins; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V; C468322:exodeoxyribonuclease V, E coli