I graduated from the University of Edinburgh in 1992 with a BSc in Biochemistry. I was then offered a place at the University of Dundee and joined David Boxer’s group studying metalloenzyme biosynthesis in bacteria. My PhD was awarded in November 1996. I then took up a postdoctoral position studying bacterial protein transport with Tracy Palmer at the John Innes Centre, Norwich. A second postdoc followed in 1998 with Ben Berks (then at the University of East Anglia) before I won a Royal Society University Research Fellowship in 2000. In prokaryotes, generation of energy by respiratory electron transfer chains involves the plasma membrane. One feature of Escherichia coli physiology is its flexible respiratory metabolism which stems from an elaborate bank of membrane-associated respiratory enzymes. Intriguingly, many respiratory enzymes are located outside of the cell cytoplasm and are often extremely complex consisting of multiple subunits and associated redox cofactors. How are such enzymes assembled and exported? Many eubacteria and archaea (and their chloroplast descendants) have the ability to transport pre-folded, very often oligomeric, and enzymatically active proteins across ionically-sealed membranes. The proteins so-transported are usually synthesised with distinctive N-terminal signal peptides that bear a common ‘twin-arginine’ SRRxFLK amino acid sequence motif. All proteins bearing twin-arginine signal peptides are transported by the twin-arginine translocation (Tat) system (1). The Tat translocase is essentially a membrane-bound nanomachine dedicated to the translocation of fully folded proteins and, depending on the biological model system under investigation, comprises 2 or 3 different membrane proteins. In E. coli, 3 types of integral membrane proteins – TatA (and its homolog TatE), TatB, TatC – are involved in the transport process (1). Two distinct Tat complexes can be isolated from resting E. coli inner membranes. TatA can be purified as a large, heterogeneous complex that also contains trace amounts of TatB (2), and the TatC protein is found in another large complex with an equimolar amount of TatB. The TatBC complex is the ‘signal recognition module’ that contains the recognition site for the twin-arginine motif on the signal peptide. Low-resolution structural analysis points to the TatA protein forming the protein-conducting channel (or ‘transport module’) of the Tat system. During protein transport a transient TatABC complex is thought to form in the membrane, but then rapidly dissociate again once the translocation of the substrate has been completed. The whole system is probably powered directly by the transmembrane proton motive force. The central dogma of Tat transport is therefore that Tat substrates are fully folded before export. As a result it is essential that biosynthesis and assembly of complex respiratory enzymes is completed in the cytoplasm before the final transport event is even attempted. A subset of Tat-targeted proteins have been found to be integral membrane proteins suggeting that the Tat translocase also has the ability to recognise and integrate transmembrane segements into the lipid bilayer (3). In addition, recent work has unearthed a mechanism that prevents premature targeting of Tat signal-bearing proteins until all biosynthetic processes are concluded. This ‘Tat proofreading’ process involves the pre-export interaction of Tat signal peptides with dedicated binding proteins (4,5). One such Tat proofreading chaperone is TorD, a small multi-functional protein, that binds tightly to the Tat signal peptide of trimethylamine N-oxide reductase (TorA) (4,5). TorD-like chaperones have a unique all-helical fold and are almost ubiquitous in bacteria and archaea. Recently, however, it has emerged that second family of peptide binding proteins, completely unrelated to TorD in terms of structure, also operates in bacteria in a Tat proofreading capacity. The NapD chaperone has a ferredoxin-like fold and binds specifically to the Tat signal peptide of nitrate reductase (NapA) preventing export until all assembly processes are complete.