5,6-Dichloro-1-beta-D-ribofuranosylbenzimidazole inhibits transcription of the beta-hemoglobin gene in vivo at initiation.

The mechanism by which 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) inhibits transcription of the beta-major Hb gene in vivo was investigated in differentiated Friend erythroleukemic cells (FELC). Steady-state nuclear RNA from untreated and DRB-treated FELC was analyzed by the S1 nuclease assay using [32P]DNA probes labeled at their 3' end close to the site of transcription initiation. DRB severely inhibited transcription of full-length beta-major Hb mRNA precursor molecules and did not increase the production of short, promoter-proximal transcripts. In addition, nascent beta-major RNA transcripts were labeled with [alpha-32P]UTP in nuclei isolated from DRB-treated FELC and untreated FELC and hybridized to separate restriction fragments spanning the entire beta-major Hb gene. DRB inhibited transcription of the promoter-proximal and promoter-distal beta-Hb DNA restriction fragments uniformly by 75-80% and did not detectably increase the amount of short transcripts. Moreover, a brief reversal of the DRB inhibition in vivo increased the number of short, nascent, promoter-proximal beta-Hb transcripts apparently as a result of reinitiation. These data indicate that DRB inhibited transcription of the beta-major Hb gene in vivo at initiation.