The induction of puff III-A3b, a major heat-shock puff in Chironomus thummi salivary cells, was insensitive to the transcription inhibitor 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole (DRB), whereas no transcriptional activity could be detected at the other heat-shock puffs in the presence of this drug. In these conditions, a polypeptide with the same Mr and isoform pattern as those of the major heat-shock polypeptide, hsp70, was synthesized. These results suggest that hsp70 is encoded by locus III-A3b. In addition to DRB insensitivity, incorporation of [3H]UTP on puff III-A3b took place in an in vitro transcription assay under low-salt conditions (100 mM NaCl); no labelling could be detected at the other heat-shock puffs under these conditions. Although DRB has been reported as a specific inhibitor of RNA polymerase II-directed transcription, and although the low-salt conditions were not propitious for the activity of this enzyme, RNA polymerase II was detected on puff III-A3b and on the other heat-shock puffs by immunofluorescence with anti-RNA polymerase II antibodies.
Studies of in vitro transcription by calf thymus RNA polymerase II using a novel duplex DNA template.
