Heat shock stabilizes highly unstable transcripts of the Xenopus ribosomal gene spacer

We have shown recently that, in Xenopus laevis oocytes, the 3' end of the longest detectable ribosomal precursor RNA is not formed by transcription termination but by RNA processing and that RNA polymerase I continues to transcribe through the intergenic spacer region. In oocytes, these spacer transcripts are turned over rapidly, and the only apparent transcription termination site is located 215 base pairs upstream of the 5' end of the next transcription unit. In this paper we show that, at heat shock temperature (34 degrees C), processing at the 3' end of the precursor, rapid turnover of spacer transcripts, and termination are all severely impaired. In contrast, transcription initiation and chain elongation are not significantly affected by heat shock. This results in the appearance of large RNA in the range of 10-20 kilobases and longer.