The eukaryotic transcription elongation factor 
5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole (DRB) sensitivity inducing 
factor (DSIF), is involved in regulating the processivity of RNA polymerase II. 
DSIF plays also a role in transcriptional activation, and in concert with the 
negative elongation factor NELF causes promoter proximal pausing of RNA 
polymerase II. Furthermore, DSIF has also been implicated in regulating the 
transcription of the human immunodeficiency virus proviral DNA. Human DSIF is 
composed of the two subunits, hSpt4 (p14) and hSpt5 (p160), corresponding to the 
yeast homologs Spt4 and Spt5. Here we show the purification and characterization 
of the small subunit, hSpt4. We were able to purify the protein in a soluble 
form separately from the larger hSpt5 subunit. CD and NMR spectroscopy show that 
the purified protein hSpt4 exhibits an alpha/beta topology with a well defined 
tertiary structure. Furthermore metal analysis by ICP-OES indicates that the 
protein contains a functional 4-Cys Zn-finger.