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Journal of Bacteriology, November 1999, p. 7021-7027, Vol. 181, No. 22
Department of Microbiology and the Groningen
Biomolecular Sciences and Biotechnology Institute, University of
Groningen, 9751 NN Haren, The Netherlands
Received 6 July 1999/Accepted 9 September 1999
Bacterial protein translocation is mediated by translocase, a
multisubunit membrane protein complex that consists of a peripheral ATPase SecA and a preprotein-conducting channel with SecY, SecE, and SecG as subunits. Like Escherichia coli SecG, the
Bacillus subtilis homologue, YvaL, dramatically stimulated
the ATP-dependent translocation of precursor PhoB (prePhoB) by the
B. subtilis SecA-SecYE complex. To systematically
determine the functional exchangeability of translocase subunits, all
of the relevant combinations of the E. coli and B. subtilis secY, secE, and secG genes were
expressed in E. coli. Hybrid SecYEG complexes were
overexpressed at high levels. Since SecY could not be overproduced
without SecE, these data indicate a stable interaction between the
heterologous SecY and SecE subunits. E. coli SecA, but
not B. subtilis SecA, supported efficient ATP-dependent
translocation of the E. coli precursor OmpA (proOmpA) into
inner membrane vesicles containing the hybrid SecYEG complexes, if
E. coli SecY and either E. coli SecE or
E. coli SecG were present. Translocation of B. subtilis prePhoB, on the other hand, showed a strict dependence
on the translocase subunit composition and occurred efficiently only
with the homologous translocase. In contrast to E. coli
SecA, B. subtilis SecA binds the SecYEG complexes only
with low affinity. These results suggest that each translocase subunit
contributes in an exclusive manner to the specificity and functionality
of the complex.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Preprotein Translocation by a Hybrid Translocase
Composed of Escherichia coli and Bacillus
subtilis Subunits
and
*
Corresponding author. Mailing address: Department of
Microbiology and the Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands. Phone: 31 503632164. Fax: 31 503632154. E-mail: A.J.M.Driessen{at}BIOL.RUG.NL.
Present address: Department of Experimental Pathology, Josephine
Nefkens Institute, Erasmus University Rotterdam. 1738 DR Rotterdam, The Netherlands.
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