Transcription elongation factor SPT4 (SUPT4H1)

Component of the DRB sensitivity-inducing factor complex (DSIF complex), which modulates mRNA processing and transcription elongation by RNA polymerase II. DSIF positively modulates mRNA capping by stimulating the mRNA guanylyltransferase activity of RNGTT/CAP1A.

DSIF also acts cooperatively with the negative elongation factor complex (NELF complex) to enhance transcriptional pausing at sites proximal to the promoter. Transcriptional pausing may facilitate the meeting of an elongation competent RNA polymerase II complex.