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We describe the identification of two Escherichia coli genes required for the export of cofactor-containing periplasmic proteins, synthesized with signal peptides containing a twin arginine motif. Both gene products are homologous to the maize HCF106 protein required for the translocation of a subset of lumenal proteins across the thylakoid membrane. Disruption of either gene affects the export of a range of such proteins, and a complete block is observed when both genes are inactivated. The Sec protein export pathway was unaffected, indicating the involvement of the gene products in a novel export system. The accumulation of active cofactor-containing proteins in the cytoplasm of the mutant strains suggests a role for the gene products in the translocation of folded proteins. One of the two HCF106 homologues is encoded by the first gene of a four cistron operon, tatABCD, and the second by an unlinked gene, tatE. A mutation previously assigned to the hcf106 homologue encoded at the tatABCD locus, mttA, lies instead in the tatB gene.

Original publication




Journal article



Publication Date





3640 - 3650


Bacterial Proteins, Base Sequence, Biological Transport, Cloning, Molecular, Cytoplasm, DNA, Bacterial, Enzyme Activation, Escherichia coli, Formate Dehydrogenases, Genes, Bacterial, Hydrogenase, Membrane Proteins, Molecular Sequence Data, Mutagenesis, Oxidoreductases, N-Demethylating, Phenotype, Plant Proteins, Protein Precursors, Protein Processing, Post-Translational, Recombinant Fusion Proteins