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J. Bacteriol. doi:10.1128/JB.01139-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Conservation and variation between Rhodobacter capsulatus and Escherichia coli Tat systems

Ute Lindenstrau and Thomas Brüser^*

Institute of Microbiology, University of Halle-Wittenberg, Kurt-Mothes-Str. 3, D-06120 Halle, Germany

^* To whom correspondence should be addressed. Email: t.brueser{at}mikrobiologie.uni-halle.de.

	Abstract

The Tat system allows the translocation of folded and often cofactor-containing proteins across biological membranes. Here we show by an inter-species transfer of a complete Tat translocon that Tat systems are largely - but not fully - interchangeable even between different classes of the proteobacteria. The Tat apparatus from the -proteobacterium Rhodobacter capsulatus was transferred to a Tat-deficient Escherichia coli strain, which is a -proteobacterium. Similar to E. coli, the R. capsulatus Tat system consists of three components, rc-TatA, rc-TatB, and rc-TatC. A fourth gene (rc-tatF) is present in the rc-tatABCF operon which has no apparent relevance for translocation. The translational starts of rc-tatC and rc-tatF overlap in four nucleotides (ATGA) with the preceding tat genes, pointing to efficient translational coupling of rc-tatB, rc-tatC, and rc-tatF. We show by a variety of physiological and biochemical assays that the R. capsulatus Tat system functionally targets the E. coli Tat substrates TorA, AmiA, AmiC, and formate dehydrogenase. Even a Tat substrate from a third organism is accepted, demonstrating that usually Tat systems and Tat substrates from different proteobacteria are compatible with each other. Only one exceptional Tat substrate of E. coli, a membrane anchored DMSO reductase, was not targeted by the R. capsulatus Tat system, resulting in a DMSO respiration deficiency. Although the general features of Tat substrates and translocons are similar between species, the data indicate that details in the targeting pathways can vary considerably.