Prokaryotic and euklaryotic cells respond to environmental stress by the induction of a variety of stress-related proteins. In mammalian cells, the most well characterized group of stress proteins are induced by hyperthermia. Transcription of heat shock proteins increases markedly after hyperthermia and several of these genes have been cloned from HeLa cells in other laboratories. It is likely that transcription of other genes is also induced in mammalian cells since approximately 10-20 genes are induced in prokaryotes and lower eukaryotes. One approach to isolate such transcripts is to enrich for heat shock specific cDNA's by hybridization subtraction with mRNA from control cells. We have done this with rodent cells, V79, and we have also constructed a cDNA library from heat shock treated (HS) cells. Our results indicate that the most abundant transcript induced by HS in V79 and CHO cell lines is a small repetitive genetic element. Sequence analysis of cDNA lines revealed that they were short RNA polymerase III transcripts of the rodent B2 repetitive element. Transcription of this repetitive element has previously been found to be increased in transformed rodent cells and rodent tumor cells. It is of interest that HS proteins are usually elevated in transformed cells. The function of this B2 RNA is unknown, but it is polyadenylated with localization to the cytoplasm; it may play some role in the regulation of translation. This hypothesis is supported by our observation that a different spectrum of B2 transcripts are transcribed after heat shock. Heat shock has profound effects on translation; e.g., preferential translation of heat shock protein RNA. We have also found that the induction of B2 RNA by heat shock correlated temporarily with the induction of the major heat shock protein RNA's.
