Elongin

Elongin is a multipart protein complex that participates in two distinct cellular processes: transcriptional elongation by RNA polymerase II and the ubiquitin ligase activity of a CRL2 complex. In humans, the elongin complex is composed of Elongin A (TCEA1), Elongin B (TCEB1), and Elongin C (TCEB2).

During transcription, Elongin A acts as the catalytic subunit of a transcription elongation factor that cooperates with ELL family proteins to stimulate RNA polymerase II elongation and to reduce promoter-proximal pausing. Elongin B and Elongin C are regulatory subunits that stabilize Elongin A and mediate protein–protein interactions needed for elongation.

Separately, Elongin B and C form part of a Cullin-2-based E3 ubiquitin ligase by associating with the VHL protein. The resulting CRL2-VHL (also called ECV) complex targets hypoxia-inducible factor alpha (HIF-1α) for ubiquitination and proteasomal degradation under normoxic conditions. Under low oxygen, HIF-1α escapes degradation, accumulates, and activates hypoxia-responsive genes.

Elongin thus participates in both gene regulation at the level of transcription elongation and cellular oxygen sensing through HIF regulation. Abnormal expression or function of the elongin components has been studied in the context of cancer and other diseases, reflecting their central roles in transcription and protein stability.