Identification and purification of the Holo-ELL complex: Evidence for the presence of ELL-associated proteins that suppress the transcriptional inhibitory activity of ELL

The human ELL gene on chromosome 19 undergoes frequent translocation with the trithorax-like MLL gene on chromosome 11 in acute myeloid leukemia. Recently, it was demonstrated that the product of the human ELL gene encodes an RNA polymerase II elongation factor (Shilatifard, A., Lane, W. S., Jackson, K. W., Conaway, R. C., and Conaway, J. W. (1996) Science 271, 1873- 1876). In addition to its elongation regulatory activity, ELL contains a novel type of RNA polymerase II interaction domain that is capable of negatively regulating polymerase activity in promoter-specific transcription in vitro (Shilatifard, A., Haque, D., Conaway, R. C., and Conaway, J. W. (1997) J. Biol. Chem. 272, 22355-22363). Here, we report the identification and purification of a large ELL-containing complex that contains three proteins in addition to ELL and that we have named the Holo-ELL complex. The Holo-ELL complex can increase the catalytic rate of transcription elongation by RNA polymerase II. However, unlike the ELL polypeptide alone, the Holo- ELL complex is not capable of negatively regulating polymerase activity in promoter-specific transcription in vitro. The inability of the Holo-ELL complex to negatively regulate polymerase activity in promoter-specific transcription suggests that one or more of the ELL-associated proteins regulate this activity, possibly through an interaction with the N-terminal domain of the ELL protein, which was shown to be required for the transcriptional inhibitory activity of ELL. Characterization of these ELL interacting proteins should help define the regulation of the biochemical activities of ELL and how loss of this regulation leads to the development of acute myeloid leukemia.