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J. Bacteriol., Jan 1995, 200-205, Vol 177, No. 1
A Matsuhisa, N Suzuki, T Noda and K Shiba
The suhB gene is located at 55 min on the Escherichia coli chromosome and
encodes a protein of 268 amino acids. Mutant alleles of suhB have been
isolated as extragenic suppressors for the protein secretion mutation
(secY24), the heat shock response mutation (rpoH15), and the DNA synthesis
mutation (dnaB121) (K. Shiba, K. Ito, and T. Yura, J. Bacteriol.
160:696-701, 1984; R. Yano, H. Nagai, K. Shiba, and T. Yura, J. Bacteriol.
172:2124-2130, 1990; S. Chang, D. Ng, L. Baird, and C. Georgopoulos, J.
Biol. Chem. 266:3654-3660, 1991). These mutant alleles of suhB cause
cold-sensitive cell growth, indicating that the suhB gene is essential at
low temperatures. Little work has been done, however, to elucidate the role
of the product of suhB in a normal cell and the suppression mechanisms of
the suhB mutations in the aforementioned mutants. The sequence similarity
shared between the suhB gene product and mammalian inositol monophosphatase
has prompted us to test the inositol monophosphatase activity of the suhB
gene product. We report here that the purified SuhB protein showed inositol
monophosphatase activity. The kinetic parameters of SuhB inositol
monophosphatase (Km = 0.071 mM; Vmax = 12.3 mumol/min per mg) are similar
to those of mammalian inositol monophosphatase. The ssyA3 and suhB2
mutations, which were isolated as extragenic suppressors for secY24 and
rpoH15, respectively, had a DNA insertion at the 5' proximal region of the
suhB gene, and the amount of SuhB protein within mutant cells decreased.
The possible role of suhB in E. coli is discussed.
Copyright © 1995, American Society for Microbiology
Inositol monophosphatase activity from the Escherichia coli suhB gene product
Research & Development Center, Fuso Pharmaceutical Industries, Osaka, Japan.
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