The Role of the rec Genes in the Viability of Escherichia coli K12
Mutations in the recA, recB, or recC genes significantly reduce the growth rate and viability of Escherichia coli. Cultures of rec − strains are composed of three populations of cells: viable cells, nonviable but residually dividing cells, and nonviable and nondividing cells. Nondividing cells can be separated from dividing cells by penicillin treatment and velocity sedimentation. Nondividing cells of all rec − strains are greatly reduced in their ability to synthesize DNA. recB − recC − and recA − recB − recC − nondividing cells contain DNA. This DNA is synthesized in dividing cells and segregated into the nondividing cells. recA −nondividing cells contain little or no DNA. recA − recB − recC − nondividing cell DNA accumulates single-strand breaks.
KeywordsVelocity Sedimentation Sucrose Gradient Fraction Number Sedimentation Pattern Nonviable Cell
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