PMID:1931824

Citation	Blakely, G, Colloms, S, May, G, Burke, M and Sherratt, D (1991) Escherichia coli XerC recombinase is required for chromosomal segregation at cell division.New Biol. 3:789-98
Abstract	XerC is a site-specific recombinase of the bacteriophage lambda integrase family that is encoded by xerC at 3700 kbp on the genetic map of Escherichia coli. The protein was originally identified through its role in converting multimers of plasmid ColE1 to monomers; only monomers are stably inherited. Here we demonstrate that XerC also has a role in the segregation of replicated chromosomes at cell division. xerC mutants form filaments with aberrant nucleotides that appear unable to partition correctly. A DNA segment (dif) from the replication terminus region of the E. coli chromosome binds XerC and acts as a substrate for XerC-mediated site-specific recombination when inserted into multicopy plasmids. This dif segment contains a region of 28 bp with sequence similarity to the crossover region of ColE1 cer. The cell division phenotype of xerC mutants is suppressed in strains deficient in homologous recombination, suggesting that the role of XerC/dif in chromosomal metabolism is to convert any chromosomal multimers (arising through homologous recombination) to monomers.
Links	PubMed
Keywords	Site-specific Recombination; Chromosome Dimers; Resolution; Binding Sites; Cell Division; Escherichia coli; Integrases; dif; cer
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Main Points of the Paper

• xerC insertion mutants have defects in cell division and chromosomal nucleoid segregation
• mutations in recA suppress the xerC^- phenotype
• site-specific recombination locus dif is related to cer (alignments included)
• dif is a substrate for XerC-mediated site-specific recombination
• XerC recombination at dif doesn't require ArgR or PepA

Materials and Methods Used

• xerC+ plasmid complementation of the xerC mutant phenotype

Phenotype Annotations

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Species	Taxon ID	Strain	Gene (if known)	OMP	Phenotype	Details	Evidence	Notes
			xerC	small colonies	Growth	on broth-containing plates	Plating Assay	xerCY17 and xerC2 are both insertion mutations
			xerC	slow recovery from stationary phase	Growth		Growth Curve	xerCY17 and xerC2 are both insertion mutations
			xerC	varying exponential growth rate	Growth	day-to-day variation of 80-100% compared to isogenic xerC+ strain	Growth Curve	xerCY17 and xerC2 are both insertion mutations
			xerC	filamented cells	Morphology	variable number of filaments	Microscopy	xerCY17 and xerC2 are both insertion mutations
			xerC	nonfilamentous cells at the two-cell stage	Morphology	excess number of these within the population	Microscopy	xerCY17 and xerC2 are both insertion mutations
			xerC	mispositioned nucleoid	Morphology	single, highly amplified nucleoid at the filament midpoint and sometimes other places within the cell	Microscopy	Fiigure 1-B2: xerCY17 and xerC2 are both insertion mutations
			xerC	abolished DNA dimer resolution	Growth	using a plasmid with dif site as a reporter for chromosome dimer resolution	Biochemical Assay	Figure 3- xerCY17 and xerC2 are both insertion mutations
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References

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