RNA polymerase II elongating complex (Pol II EC)

The elongating phosphorylated RNA polymerase II (Pol II) complex is the active molecular machinery responsible for transcribing DNA into messenger RNA. This complex is characterized by specific phosphorylation patterns on the C-terminal domain (CTD) of its largest subunit, RPB1, particularly at Serine 2 and Serine 5 positions, which facilitate recruitment of elongation and splicing factors (Svejstrup, 2002). When this complex encounters DNA adducts—covalent modifications caused by UV radiation or chemotherapeutic agents like cisplatin—it becomes physically stalled, especially in promoter-proximal regions where pausing is frequent (Wilson et al., 2023). This stalling event is a critical biological signal that triggers transcription-coupled nucleotide excision repair (TC-NER), a pathway dedicated to removing lesions that obstruct transcription. In oncology, the persistence of stalled Pol II complexes at DNA adducts is a primary mechanism of action for platinum-based chemotherapy, as unresolved stalls lead to DNA double-strand breaks and programmed cell death (Jung & Lippard, 2007). Conversely, mutations in proteins that recognize or process these stalled complexes, such as CSB or CSA, result in severe ribosomopathies and DNA repair disorders like Cockayne syndrome, which are marked by extreme sun sensitivity and premature aging. Targeting the stability or phosphorylation state of this complex remains a significant area of therapeutic interest, particularly through the use of CDK inhibitors and next-generation DNA-damaging agents (Garriga & Grana, 2004).

Other names

Stalled RNA polymerase II complexPhosphorylated RNA polymerase IIPol IIOTranscription-coupled repair complexRNA polymerase II holoenzyme

Platinum-based agents create bulky DNA adducts that physically block the progression of the elongating Pol II complex, leading to persistent stalling and the induction of apoptosis (Jung & Lippard, 2007). CDK9 inhibitors (e.g., Flavopiridol) prevent the C-terminal domain (CTD) phosphorylation required for the transition from initiation to productive elongation, effectively inhibiting the formation of the active complex (Garriga & Grana, 2004).