Journal of Bacteriology, May 2000, p. 2771-2777, Vol. 182, No. 10
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
B Stress Response
Transcription Factor Cofractionate with Ribosomes

Department of Microbiology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900
Received 30 November 1999/Accepted 15 February 2000
Obg, an essential GTP binding protein of Bacillus
subtilis, is necessary for stress activation of the
B transcription factor. We investigated Obg's cellular
associations by differential centrifugation of crude B. subtilis extracts, using an anti-Obg antibody as a probe to
monitor Obg during the fractionation, and by fluorescent microscopy of
a B. subtilis strain in which Obg was fused to green
fluorescent protein. The results indicated that Obg is part of a large
cytoplasmic complex. In subsequent analyses, Obg coeluted with
ribosomal subunits during gel filtration of B. subtilis
lysates on Sephacryl S-400 and specifically bound to ribosomal protein
L13 in an affinity blot assay. Probing the gel filtration fractions
with antibodies specific for
B and its coexpressed
regulators (Rsb proteins) revealed coincident elution of the upstream
components of the
B stress activation pathway (RsbR, -S,
and -T) with Obg and the ribosomal subunits. The data implicate
ribosome function as a possible mediator of the activity of Obg and the
stress induction of
B.
Present address: Department of Food Science and Technology,
University of Nebraska, Lincoln, NE 68585-0919.
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