In
gene expression,
DSIF (
DRB Sensitivity Inducing Factor) is a
protein that can either negatively or positively affect transcription by
RNA polymerase II (Pol II). In one case of negative regulation, it can interact with
negative elongation factor (NELF) to promote the stalling of Pol II at some genes. This stalling is relieved by
P-TEFb. In humans, DSIF is composed of
hSPT4 and
hSPT5 (SPT4 and SPT5 are homologs in yeast).