1H, 13C, and 15N resonance assignments and solution structure of the CID domain of SR-related- and CTD-associated factor 8 (SCAF8)

Abstract

Transcription mediated by RNA polymerase II (RNAPII) involves multiple stages, including initiation, promoter-proximal pausing for capping, elongation, and termination. The C-terminal domain of RNAPII (CTD) contains repetitions of the heptad consensus sequence, such as Y₁S₂P₃T₄S₅P₆S₇ with some variety, and the phosphorylated positions in the heptad sequences are altered according to the transcriptional stages. The interaction between several regulatory protein factors and the phosphorylated heptad sequence plays an important role in the accurate progress of transcription. A subset of these regulatory proteins possesses a CTD-interacting domain (CID) that specifically recognizes the phosphorylated CTD and mediates stage-specific transcriptional control. Among them, SCAF8 (RBM16), which also contains a CID, plays a key role in accurate transcriptional termination in conjunction with its paralog SCAF4. Despite their importance, the precise molecular mechanisms through which SCAF8 and SCAF4 coordinate transcriptional termination via their CID domains remain poorly understood. In this study, we report the ¹H, ¹⁵N, and ¹³C NMR resonance assignments and solution structure of the human SCAF8 CID domain. The structure exhibits an α1–α2–α3–α4–α5–α6–α7–α8 helical topology, consistent with the previously determined crystal structure. These assignments provide a valuable foundation for understanding how SCAF8 interacts with the RNAPII CTD and contributes to transcriptional elongation and termination.