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J. Bacteriol., Nov 1995, 6064-6068, Vol 177, No. 21
Y Yamada, M Yamada and A Nakazawa
To detect entry exclusion of the ColE1 plasmid, we established an assay
system that was not influenced by incompatibility of extant plasmids in the
recipient cells or by the viability of the cells due to the killing action
of colicin E1 protein. The assay revealed that exc1 and exc2, assigned as
genes directing entry exclusion, had no exclusion activity. Instead, mbeD,
which had been characterized as a gene for plasmid mobilization, directed
the exclusion activity. MbeD was overexpressed and identified as a
35S-labeled protein, which was recovered in both the soluble and membrane
fractions, particularly in the inner membrane fraction. An amphipathic
helical structure was predicted in the N- terminal region of MbeD as well
as in the corresponding homologous proteins of ColA and ColK. These
proteins may bind to the inner membrane via the N-terminal amphipathic
helix and function in entry exclusion.
Copyright © 1995, American Society for Microbiology
A ColE1-encoded gene directs entry exclusion of the plasmid
Department of Biochemistry, Yamaguchi University School of Medicine, Japan.
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