DEAD-box RNA helicases in Escherichia coli

In spite of their importance in RNA metabolism, the function of DExD/H-box proteins (including DEAD-box proteins) is poorly understood at the molecular level. Here, we present recent progress achieved with the five DEAD-box proteins from Escherichia coli, which have been particularly well studied. These proteins, which have orthologues in many bacteria, participate, in particular, in specific steps of mRNA decay and ribosome assembly. In vitro, they behave as poorly processive RNA helicases, presumably because they only unwind a few base pairs at each cycle so that stable duplexes can reanneal rather than dissociate. Except for one of them (DbpA), these proteins lack RNA specificity in vitro, and specificity in vivo is likely conferred by partners that target them to defined substrates. Interestingly, at least one of them is multifunctional, presumably because it can interact with different partners. Altogether, several aspects of the information gathered with these proteins have become paradigms for our understanding of DEAD-box proteins in general.