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I have read that the termination of the transcription of mRNA involves a termination sequence in the form of a stem loop. As the structure of ribosomal RNA involves extensive internal base pairing, I wonder whether part of the mature rRNA provides the termination loop for its transcription.

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  • $\begingroup$ Your question is unclear to me. You question appears to be about the termination of transcription of rRNA, although your title seems to be about rRNA structure that can be answered from any book or Wikiipedia. Your tag of reverse-transcription was certainly wrong and I have removed it. Please clarify your question, but first do some reading. A statement that "I know rRNA must come from a gene" suggests you might benefit from this. $\endgroup$ – David Mar 14 '18 at 0:06
  • $\begingroup$ As you haven't replied and as nobody else followed my vote to close this question I have rewritten it in a way that now makes some sense and may be what you meant. If not please edit it. I have reversed my close vote and will answer the question if nobody else does. $\endgroup$ – David Mar 16 '18 at 23:09
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Summary

The process of the termination of transcription is still not well understood. It differs between eukaryotes and prokaryotes and between mRNA and rRNA. Although it involves stem-loop structures, such structures may be necessary, but are not sufficient for termination. The idea that the termination signal might be part of the mature functional transcript — especially for rRNA comes up against a number of problems, and turns out to be incorrect. Such problems include the extensive nature of the stem loops (which to use?) and the fact that the smaller stem loops emanating from the core conserved hydrogen-bonded skeleton, are not necessarily themselves conserved (reviewed by Brimacombe). In fact the large and small rRNAs are in a single transcription unit with other genes at the end of which are specific termination signals outside the region encoding the mature rRNA.

Prokaryotic rRNA transcription

This has been reviewed by Condon, Squires and Squires (1995). The structure of the well-studied rrnB operon of E.coli is shown below, with the promoters indicated as ‘P1’and P2’ and the terminator sequences as ‘T1’ and ‘T2’. (Adapted from Pfeiffer and Hartmann.)

rrnB operon structure

This transcription unit includes the 5S rRNA as well as a tRNA.

Eukaryotic rRNA transcription

This has been reviewed by Goodfellow and Zoomerdijk(2012), from which the diagram below, of the mammalian rDNA repeat, is taken. The terminator elements are ‘T1–10’.

eukaryotic ribosomal DNA repeat

In eukaryotes the 5S rRNA is not in the same transcription unit as the large and small rRNAs (and the 5.8S rRNA). Indeed it is transcribed by DNA-dependent RNA polymerase III, rather than the DNA-dependent RNA polymerase I, which transcribes the rDNA repeat shown.

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Transfer RNAs (rRNAs), ribosomal RNAs (rRNAs) all fold back on themselves and hydrogen bond to make complementary base pairs. So yes, this is common.

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  • $\begingroup$ I think that, despite the title, the question is about termination of rRNA transcription, not rRNA structure. On reflection, he is probably asking if the transcription termination loop (if such exists for rRNA — I don't know) is part of the rRNA transcript and (perhaps) the mature processed rRNA. $\endgroup$ – David Mar 14 '18 at 0:10
  • $\begingroup$ Apologies, but I edited the question so that your answer is no longer pertinent. As it is just a two-liner, I trust it will not inconvenience you too much. $\endgroup$ – David Mar 16 '18 at 23:09

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