The RNA polymerase II core subunit 11 interacts with keratin 19, a component of the intermediate filament proteins

We have previously cloned the human RNA polymerase II subunit 11, as a doxorubicin sensitive gene product. We suggested multiple tasks for this subunit, including structural and regulatory roles. With the aim to clarify the human RNA polymerase II subunit 11 function, we have identified its interacting protein partners using the yeast two-hybrid system. Here, we show that human RNA polymerase II subunit 11 specifically binds keratin 19, a component of the intermediate filament protein family, which is expressed in a tissue and differentiation-specific manner. In particular, keratin 19 is a part of the nuclear matrix intermediate filaments. We provide evidence that human RNA polymerase II subunit 11 interacts with keratin 19 via its N-terminal alpha motif, the same motif necessary for its interaction with the human RNA polymerase II core subunit 3. We found that keratin 19 contains two putative leucine zipper domains sharing peculiar homology with the alpha motif of human RNA polymerase II subunit 3. Finally, we demonstrate that keratin 19 can compete for binding human RNA polymerase II subunit 11/human RNA polymerase II subunit 3 in vitro, suggesting a possible regulatory role for this molecule in RNA polymerase II assembly/activity.