5,6-Dichloro-1-ß-D-ribofuranosylbenzimidazole (DRB) is a chemical compound that inhibits transcription elongation by RNA Polymerase II. Sensitivity to DRB is dependent on DRB sensitivity inducing factor (DSIF), negative elongation factor (NELF), and positive transcription elongation factor b (P-TEFb). DRB is a nucleoside analog and also inhibits some protein kinases.