Selenomethionine incorporation in Saccharomyces cerevisiae RNA polymerase II

A protocol for the incorporation of SeMet into yeast proteins is described. Incorporation at a level of about 50% suffices for the location of Se sites in an anomalous difference Fourier map of the 0.5 MDa yeast RNA polymerase II. This shows the utility of the approach as an aid in the model-building of large protein complexes.