Heat shock alters poly(A) tail length of Dictyostelium discoideum hsp32 RNA

Hsp32 is a heat shock gene in D. discoideum. We have previously observed that heat stress-induced change produces a broad band on Northern blots, suggesting that more than one population of mRNA is present under those conditions. This was not the result of a defect in the splicing of the hsp32 mRNA, nor did it result from the use of a different transcription start site under heat shock conditions. Here, we show that the broad banding pattern reflects the appearance of a transcript with a poly(A) tail that is approximately 100 nt longer than that seen in unstressed cells. Experiments indicated that this tail was not a property of newly synthesized mRNA but rather a response to heat stress. This response appeared to be specific to the hsp32 transcript and did not result in the retention of the RNA in the nucleus. These results document a relatively unusual heat shock response and also indicate that the nature of the response differs among RNAs and has selective consequences.