Previously, we have described the expression of ets-1 and ets-2 proto-oncogene products in E. coli using heat-inducible expression vectors. Although we were able to express large quantities of the recombinant protein products, the E. coli ets proteins were found to be insoluble and present in inclusion bodies. To circumvent the solubility problems, we have now constructed vectors that will allow us to produce protein products in vitro using rabbit reticulocyte lysates. Although this in vitro system does not produce large quantities of proteins, the proteins are soluble and can be readily tested for biochemical activities such as protein:DNA interaction, as well as protein:protein interaction. For example, immunoglobulin enhancer binding proteins, E12 and E47, expressed in this reticulocyte in vitro system, have been demonstrated to bind to DNA, and also to form protein-protein homo- and hetero-dimers. In some cases, post-translational modification may also be important for testing the product's biochemical activity; previous reports indicated that baculoviral vectors express high levels of products that are post-translationally processed products in the insect cells. Thus, to produce large quantities of native, processed ets proteins we have constructed a vector that is capable of producing the ets-2 product in baculovirus-infected SF9-insect cells. The proteins expressed by these baculoviral vectors are now being tested for biochemical activity.
