FIG. 2.
Replacement of repeats 1 to 3 by consensus repeats induces degradation to Pol IIb. Deletion and substitution mutants of repeats 1 to 3 were created both in the wt and Δ50 backgrounds. Mutants 2 and 6 contain a substitution of repeats 1 to 3 for a motif from Abl1 (CTD-ID), known to interact with CTD52 (sequences shown below). Similarly, mutants 3 and 7 contain a random linker of the same length. In mutants 4 and 8, repeats 1 to 3 were replaced by repeat 52 flanked at each side by a consensus repeat. Stable Raji cell lines were produced for each mutant; after expression, cells were cultivated 48 h in the presence of α-amanitin before being harvested, and the different forms produced by each mutant were separated by polyacrylamide gel electrophoresis, followed by Western analysis. The Western blot reveals the different forms produced by each mutant; stability is summarized in the right-hand column.