Fig. 4. Sat III transcripts are associated with Sm proteins. (A) SnRNPs (green) were detected in non heat-schocked and heat-shocked HeLa cells together with HSF1 (red). SnRNPs were not recruited to the stress granules although they were not excluded from these regions. Bar: 5 µm. (B) The endogenous snRNPs proteins were immunoprecipitated from non heat-shocked or heat-shocked cells with a specific monoclonal antibody (clone Y12). Co-immunoprecipitated RNAs were extracted and analyzed by reverse transcription as previously described. In non heat-shocked cells (37°C), a strong signal for the constitutively expressed hsp90 transcripts and faint signals for hsp70 and sat III transcripts were observed. In cells that were heat-shocked for 1 hour at 42°C or that were allowed to recover for 3 hours at 37°C following heat shock (rec), a strong signal is obtained for hsp90 and sat III transcripts but not for the intronless hsp70 transcripts, thus showing that hsp90 and sat III transcripts are present in vivo in a complex with snRNPs. As expected, no significant signal was obtained with the sense primer to hsp90 transcripts.