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J. Bacteriol., 07 1996, 3854-3859, Vol 178, No. 13
T Yasuda, T Nagata and H Ohmori
The Escherichia coli strain cs2-68 is a cold-sensitive (c) mutant that
forms a long filamentous cell at 20 degrees C with a large nucleoid mass in
its central region. We have recently shown that the pcsA68 mutation causing
the cs phenotype is a single-base substitution within the dinD gene, a DNA
damage-inducible gene which maps at 82 min. Since null mutants of the pcsA
(dinD) gene are viable, with no discernible defect in cell growth, the cs
phenotype is attributed to a toxic effect by the mutant protein. In an
attempt to identify a target(s) for the toxic pcsA68 mutant protein, we
screened for chromosomal fragments on multicopy plasmids that could
suppress the cs phenotype. Three different BamHI fragments were found to
suppress cold sensitivity, and the lexA, dinG, and dinI genes were
identified to be responsible for the suppression in each fragment. DinG
shares multiple motifs with many DNA helicases. The complete sequence of
dinI revealed that DinI is a small protein of 81 amino acids. It is similar
in size and sequence to ImpC of the Salmonella typhimurium plasmid TP110
and to a protein (ORFfs) of the retronphage phi R67, both of which are also
under the control of LexA.
Copyright © 1996, American Society for Microbiology
Multicopy suppressors of the cold-sensitive phenotype of the pcsA68 (dinD68) mutation in Escherichia coli
Institute for Virus Research, Kyoto University, Japan.
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