Transcription of ribosomal DNA by RNA polymerase I is a central feature of eukaryotic ribosome biogenesis. Since ribosome synthesis is closely linked to cell proliferation, there is a need to define the molecular mechanisms that control transcription by RNA polymerase I. To fully define the factors that control RNA polymerase I activity, biochemical analyses using purified transcription factors are essential. Although such assays exist, one limitation is the low abundance and difficult purification strategies required for some of the essential transcription factors for RNA polymerase I. Here, we describe a new method for expression and purification of the three subunit core factor complex from Escherichia coli. We demonstrate that the recombinant material is more active than yeast-derived core factor in assays for RNA polymerase I transcription in vitro. Finally, we use recombinant core factor to differentiate between two opposing models for the role of the TATA-binding protein in transcription by RNA polymerase I. © 2011 Elsevier B.V.