Transcription Factors of RNA Polymerase III from Mammalian Cells

RNA polymerase III presents a versatile experimental system for the analysis of eukaryotic transcription. Transcription complexes can be generated in vitro from a limited number of transcription factors and they can subsequently be isolated in a complete and fully functional form. The analysis of the essential DNA-protein and protein-protein interactions underlying the formation of such complexes requires the purification of the transcription factors involved. We succeeded to purify TFIIIA, TFIIIB and TFIIIC from HeLa cells and describe here some of their properties. TFIIIA from human cells is structurally and immunologically different from its functionally equivalent counterpart in Xenopus laevis oocytes. This raises interesting questions with regard to the structure-function relationship of these two proteins. TFIIIC, purified from HeLa cells, was shown for the first time to primarily and specifically interact with the gene for ribosomal 5S RNA. These results could shed light onto the hitherto unknown but essential role of TFIIIC during the synthesis of ribosomal 5S RNA. The long-term goal of our investigations is to clone the genes coding for the polIII transcription factors and to study their expression during different stages of growth and differentiation.