NEWS VIEWS to which strong interactions become weak at very short distances In this perturbative regime we understand at least in principle how to work with QCD But for the strong coupling that occurs over larger distances one has to resort to computer simulation techniques known as lattice QCD These techniques have been rather successful for instance in explaining the spectrum of hadron masses but rigorous results remain hard to come by despite years of effort we still cannot explain for example why there are no free single quarks in nature Such unresolved puzzles are coming into renewed focus with the scheduled start of experiments at the Large Hadron Collider at CERN in Geneva next year The new approach that revives the link to string theory first suggested itself in 1998 when Juan Mart n Maldacena conjectured12 a link between a close relative of QCD and a superstring living in a ten dimensional curved space time Although the theory in question known as supersymmetric N 4 gauge theory is sufficiently different from QCD to be of no direct interest to experiment the link raised the prospect of a general connection to some form of compactified string theory This equivalence is now commonly referred to as the AdS CFT Anti de Sitter conformal field theory correspondence If true it would mean that string theory was originally not so far off the mark after all its ingredients just need to be interpreted in the correct way The Maldacena conjecture raised a lot of interest but seemed for a long time to be quantitatively unverifiable This was because it takes the form of a duality in which the strongly coupled string theory corresponds to weakly coupled QCD like theory and vice versa But to verify the duality one would need to find a quantity to compare in a regime of intermediate coupling strength and calculate it starting from both sides No such quantity was obvious Help came from an entirely unexpected direction Following a prescient observation13 the spectrum of the N 4 theory has been found1 2 to be equivalently described by a quantum mechanical spin chain of a type discovered by Hans Bethe in 1931 when modelling certain metallic systems There are not many quantum mechanical systems that can be solved analytically the hydrogen atom is the most prominent example but Bethe s ansatz immediately applied in a much wider context and constructed a bridge between condensed matter physics and string theory in this context see the recent News Views article by Jan Zaanen14 on the nascent connection to high temperature superconductivity Indeed even though the mathematical description of the duality on the string theory side is completely different from that on the condensed matter side a very similar exactly solvable structure has been identified here as well3 5 Puzzling out the details of the exact solution 798 NATURE Vol 449 18 October 2007 is currently an active field of research But in one instance that idea had already been put to such a hard test that a complete solution now seems within reach The context is a special observable entity the cusp anomalous dimension which was argued6 7 to be ideally suited as a device to test whether string and gauge theory really connect Some of its structure at strong coupling was also worked out Just recently Beisert Eden and Staudacher8 have extracted the analogue of this observable on the field theory side and have been able to write down an equation valid at any strength of the coupling Since then work has established that their BES equation does indeed seem for the first time to offer a means of reformulating theories such as QCD as string theories Much still needs to be learned from this one exactly solvable case There is justifiable hope that this solution will teach us how to go back to the physically relevant case of QCD and finally arrive at the long sought dual description by a string theory It may even take us closer to realizing the quantum field theorist s ultimate dream unfulfilled for more than 50 years completely understanding an interacting relativistic quantum field theory in the four space time dimensions that we are familiar with Progress towards this goal can be judged independently of loftier attempts to use strings in the construction of a theory of everything Hermann Nicolai is at the Max Planck Institut f r Gravitationsphysik Albert Einstein Institut M hlenberg 1 D 14476 Potsdam Germany e mail nicolai aei mpg de 1 Minahan J A Zarembo K J High Energy Phys 0303 013 2003 2 Beisert N Kristjansen C Staudacher M Nucl Phys B 664 131 184 2003 3 Bena I Polchinski J Roiban R Phys Rev D 69 046002 2004 4 Kazakov V A Marshakov A Minahan J A Zarembo K J High Energy Phys 0405 024 2004 5 Arutyunov G Frolov S Staudacher M J High Energy Phys 0410 016 2004 6 Gubser S S Klebanov I R Polyakov A M Nucl Phys B 636 99 114 2002 7 Frolov S Tseytlin A A J High Energy Phys 0206 007 2002 8 Beisert N Eden B Staudacher M J Stat Mech P01021 2007 9 Veneziano G Nuovo Cimento 57A 190 1968 10 Ramond P Phys Rev D 3 2415 2418 1971 11 Neveu A Schwarz J H Nucl Phys B 31 86 112 1971 12 Maldacena J M Adv Theor Math Phys 2 231 252 1998 13 Lipatov L N preprint available at www arxiv org abs hep th 9311037 1993 14 Zaanen J Nature 448 1000 1001 2007 MICROBIOLOGY Preparing the shot Christof R Hauck Direct injection of proteins into host cells is one of the tricks bacteria use during infection It seems that to achieve this the stomach pathogen Helicobacter pylori first grabs the cell by its surface receptors The bacterium Helicobacter pylori successfully colonizes the stomach of about every third person Infection with this ubiquitous microorganism can cause acute and chronic gastritis as well as stomach ulcers1 Moreover up to 90 of cases of stomach cancer are associated with H pylori infection The bacterium s main weapon is an elaborate apparatus on its surface called the type IV secretion system which acts as a nano syringe Fig 1a Using this apparatus the bacterium delivers a cancerassociated protein CagA directly into its host cells But whether the bacterium anchors the secretion system to the surface of host cells before injection and if so how has remained unclear On page 862 of this issue Kwok et al 2 report that transfer of CagA is made possible by another H pylori protein CagL which binds to integrin receptors on gastric epithelial cells So far CagA is the only H pylori protein known to be injected into the host cell In the bacterial chromosome the cagA gene is part