Regulation of the transcription of heat shock genes in nuclei from soybean (Glycine max) seedlings

Run‐off transcription in nuclei isolated from soybean seedlings was used to test the hypothesis that the expression of heat shock genes is controlled at the level of transcription. Only nuclei p retreated by a heat shock at 41°C prior to their isolation synthesized RNA from heat shock genes. The specificity of transcripts was determined by Southern blot hybridization of [ 32 P]‐labelled run‐off RNA with DNA fragments from several heat shock and non‐heat shock genes. The strand selectivity of heat shock gene transcription was exemplified by single stranded DNA probes. Low concentrations of α‐amanitin completely inhibited the synthesis of heat shock specific RNA, but only partially inhibited the synthesis of ribosomal RNA. The overall transcription of nuclei isolated from heat shock tissue was reduced by more than 20% compared to that in nuclei from control tissue. This decline is consistent with a decrease in the transcriptional activity of non‐heat shock genes transcribed by RNA polymerases I and II. Our results suggest that temperature stress induces the transcriptional activation of heat shock genes and has a negative effect on the transcription of other genes.