NMR assignment of the intrinsically disordered C-terminal region of Homo sapiens FCP1 in the unbound state

The phosphorylation state of the RNA polymerase II C-terminal repeat domain (CTD) regulates progression through the mRNA biogenesis cycle. Termination of transcription and recycling of RNA polymerase II is promoted by an interaction between the general transcription factor IIF (TFIIF) and the TFIIF-associating CTD phosphatase (FCP1). The acidic C-terminal region of FCP1 is disordered in the free state, but adopts an α-helical conformation upon binding to the heavy chain of TFIIF. Here we report ¹H, ¹³C, and ¹⁵N resonance assignments for the intrinsically disordered unbound form of human C-terminal FCP1 (residues 879-961). The use of recently developed ¹³C direct detected "protonless" NMR experiments allowed the nearly complete assignment of FCP1 reported here and is likely to be a generally effective strategy for the chemical shift assignment of disordered proteins.