Induction of B2 RNA polymerase III transcription by heat shock: enrichment for heat shock induced sequences in rodent cells by hybridization subtraction.

When hybridization subtraction was used to enrich for sequences induced by heat shock in Chinese hamster cells, B2 sequences were found to be one of the major sequences enriched. With cloned B2 probes, we found that the level of the short, 0.1 to 0.6 kb, polyadenylated RNA polymerase III transcripts of this repetitive genetic element increased approximately 10 to 20 fold after heat shock. Transcription of B2 RNA by RNA polymerase III was rapidly induced after heat shock based on time course studies and nuclear runoff experiments. The induction of B2 RNA was not a nonspecific response to lethality or cellular injury because maximum B2 RNA induction was observed with even nontoxic heating while no induction occurred with other agents such as UV or X-radiation. Since B2 RNA increased after heat shock in several different Chinese hamster and mouse cell lines, induction of B2 RNA by heat shock is probably common in rodent cells. B2 RNA may also be the most abundant transcript induced by heat shock because the level of B2 RNA was substantially higher than several other abundant transcripts induced by heat shock including a rodent HSP70. Our finding of the induction of high levels of RNA polymerase III B2 transcripts in different rodent cells raise the possibility of a role in the heat shock response.