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J. Bacteriol., 01 1997, 170-179, Vol 179, No. 1
S Okamoto, M Itoh and K Ochi
Morphological differentiation in microorganisms is usually accompanied by a
decrease in intracellular GTP pool size, as has been demonstrated in
bacillaceae, streptomycetaceae, and yeasts. The obg gene, which codes for a
GTP-binding protein belonging to the GTPase superfamily of proteins, was
cloned from Streptomyces griseus IFO13189. The gene is located just
downstream of the genes for ribosomal proteins L21 and L27, encoded a
protein of 478 amino acids (51 kDa), and possessed three consensus motifs
which confer GTP-binding ability; Obg protein expressed in Escherichia coli
bound GTP, as demonstrated using a UV cross-linking method. Introduction of
multiple copies of obg into wild- type S. griseus suppressed aerial
mycelium development in cells on solid media. However, no effect on
streptomycin production was detected, indicating that Obg is involved in
the regulation of the onset of morphological but not physiological
differentiation. Multiple copies of obg also suppressed submerged spore
formation in liquid culture. Southern hybridization studies indicated that
genes homologous to obg exist widely in streptomycetes, and an obg homolog
was successfully cloned from S. coelicolor A3(2). We propose that by
monitoring the intracellular GTP pool size, the Obg protein is involved in
sensing changes in the nutritional environment leading ultimately to
morphological differentiation.
Copyright © 1997, American Society for Microbiology
Molecular cloning and characterization of the obg gene of Streptomyces griseus in relation to the onset of morphological differentiation
National Food Research Institute, Tsukuba, Ibaraki, Japan.
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