Transcription elongation factor SPT5-RNA polymerase II complex (SPT5-Pol II complex)

The Spt5-RNA polymerase II complex is a fundamental molecular assembly responsible for the regulation of gene transcription in eukaryotic cells. Spt5, a key subunit of the DRB sensitivity-inducing factor (DSIF), interacts directly with RNA polymerase II (Pol II) to modulate the enzyme's processivity and speed during the elongation phase of transcription (Citations: UniProt P49336; PubMed: 30046036). Initially, the Spt5-Pol II interaction facilitates promoter-proximal pausing, a critical checkpoint that ensures proper mRNA capping and prepares the complex for productive elongation. Upon phosphorylation by the Positive Transcription Elongation Factor b (P-TEFb) complex, Spt5 undergoes a conformational shift that transforms it into a positive elongation factor, enabling the synthesis of full-length transcripts (Citations: Nature, 2018, 557(7704):267-271). Dysregulation of this complex is implicated in various diseases, most notably in cancer, where it supports the rapid expression of oncogenes like MYC, and in viral infections such as HIV-1, where the virus hijacks the complex to promote its own genomic replication (Citations: Cell, 2017, 169(4):605-618). Consequently, the Spt5-Pol II interface and its regulatory kinases, such as CDK9, are major focal points for therapeutic intervention using small-molecule inhibitors designed to disrupt aberrant transcriptional programs (Citations: Clinical Cancer Research, 2020, 26(11):2713-2721).

Other names

DSIF-RNA polymerase II complexSUPT5H-RNA polymerase II complexSpt4/5-Pol II complexTranscription elongation factor Spt5-RNA polymerase II complex

Inhibition of CDK9 or CDK7 kinases prevents the phosphorylation of Spt5 and the RNA polymerase II C-terminal domain, thereby blocking the transition from promoter-proximal pausing to productive elongation and suppressing the expression of short-lived oncogenic mRNAs.