IDENTIFICATION OF ELONGIN-C SEQUENCES REQUIRED FOR INTERACTION WITH THE VON-HIPPEL-LINDAU TUMOR-SUPPRESSOR PROTEIN

Elongin C is a 112-amino acid protein that is found in mammalian cells as a positive regulatory subunit of heterotrimeric RNA polymerase ll elongation factor Elongin (Sill) and as a component of a multiprotein complex containing the von Hippel-Lindau (VHL) tumor suppressor protei n, As a subunit of the Elongin complex, Elongin C interacts directly w ith the transcriptionally active Elongin A subunit and potently induce s its elongation activity; in addition, Elongin C interacts with the u biquitin-like Elongin B subunit, which regulates the interaction of El ongin C with Elongin A, As a component of the VHL complex, Elongin C i nteracts directly with both Elongin B and the VHL, protein. Binding of the VHL protein to Elongin C was found to prevent Elongin C from inte racting with and activating. Elongin A in vitro, leading to the propos al that one function of the VHL protein may be to regulate RNA polymer ase II elongation by negatively regulating the Elongin complex. In thi s report, we identify Elongin C sequences required for its interaction with the VHL protein, We previously demonstrated that the ability of Elongin C to hind and activate Elongin A is sensitive to mutations in the C-terminal half of Elongin C, as well as to mutations in an N-term inal Elongin C region needed for formation of the Elongin BC complex. Here we show that interaction of Elongin C with the VHL tumor suppress or protein depends strongly on sequences in the C terminus of Elongin C but is independent of the N-terminal Elongin C region required for b inding to Elongin B and for binding and activation of Elongin A. Taken together, our results are consistent with the proposal that the VHL p rotein negatively regulates Elongin C activation of the Elongin comple x by sterically blocking the interaction of C-terminal Elongin C seque nces with Elongin A. In addition, our finding that only a subset of El ongin C sequences required for its interaction with Elongin A are crit ical for binding to VHL may offer the opportunity to develop reagents that selectively interfere with Elongin and VHL function.