Use of lactose to induce expression of soluble NifA protein domains of Herbaspirillum seropedicae in Escherichia coli

Overexpression and purification are procedures used to allow functional and structural characterization of proteins. Many overexpressed proteins are p artially or completely insoluble, and can not be easily purified. The NifA protein is an enhancer-binding protein involved in activating the expressio n of nif and some fix genes. The NifA protein from many organisms is usuall y insoluble when over-expressed, and therefore difficult to work with in vi tro. In this work we have overexpressed the central+C-terminal and the cent ral domains of the Herbaspirrilum seropedicae NifA protein in an Escherichi a coli background. Expression was induced with either IPTG or lactose. The data showed that induction with lactose promoted a significantly higher per centage of these proteins in the soluble fraction than with IPTG. This prob ably reflects a slower kinetics of induction by lactose.