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.     

Inhibitory effect of long chain fatty acyl CoAs on RNA polymerase from Escherichia coli

RNA polymerase from Escherichia coli was inhibited by long chain fatty acyl CoAs, such as myristoyl CoA (Ki = 17.2 microM), palmitoyl CoA (Ki = 8.9 microM), oleoyl CoA (Ki = 5.5 microM), and stearoyl CoA (Ki = 0.94 microM). The inhibition by these CoA thioesters was non-competitive against nucleoside triphosphates. Short chain fatty acyl CoAs, such as acetyl CoA, propionyl CoA, acetoacetyl CoA, butyryl CoA, and decanoyl CoA, failed to inhibit RNA polymerase. CoA, Na-myristate, Na-palmitate, Na-oleate, Na-stearate, palmitoyl carnitine, and carnitine did not inhibit the enzyme. The inhibition of RNA polymerase by long chain fatty acyl CoAs was competitive against template DNA.