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J. Bacteriol., Apr 1996, 2044-2050, Vol 178, No. 7
DC Pecota and TK Wood
The hok (host killing) and sok (suppressor of killing) genes (hok/sok)
efficiently maintain the low-copy-number plasmid R1. To investigate whether
the hok/sok locus evolved as a phage-exclusion mechanism, Escherichia coli
cells that contain hok/sok on a pBR322-based plasmid were challenged with
T1, T4, T5, T7, and lambda phage. Upon infection with T4, the optical
density of cells containing hok/sok on a high-copy- number plasmid
continued to increase whereas the optical density for those lacking hok/sok
rapidly declined. The presence of hok/sok reduced the efficiency of plating
of T4 by 42% and decreased the plaque size by approximately 85%.
Single-step growth experiments demonstrated that hok/sok decreased the T4
burst size by 40%, increased the time to form mature phage (eclipse time)
from 22 to 30 min, and increased the time to cell lysis (latent period)
from 30 to 60 min. These results further suggest that single cells exhibit
altruistic behavior.
Copyright © 1996, American Society for Microbiology
Exclusion of T4 phage by the hok/sok killer locus from plasmid R1
Department of Chemical and Biochemical Engineering, University of California, Irvine, 92717-2575, USA.
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