Nucleic Acids Research, Vol 24, Issue 23 4725-4732, Copyright © 1996 by Oxford University Press
JH Doelling and CS Pikaard
Rapid evolution of ribosomal RNA (rRNA) gene promoters often prevents their
recognition in a foreign species. Unlike animal systems, we show that
foreign plant rRNA gene promoters are recognized in an alien species, but
tend to program transcription by a different polymerase. In plants, RNA
polymerase I transcripts initiate at a TATATA element (+1 is underlined)
important for promoter strength and start-site selection. However,
transcripts initiate from +32 following transfection of a tomato promoter
into Arabidopsis. The rRNA gene promoter of a more closely related species,
Brassica oleracea, programs both +1 and +29 transcription. A point mutation
at +2 improving the identity between the Brassica and Arabidopsis promoters
increases +1 transcription, indicating a role for the initiator element in
species- specificity. Brassica +29 transcripts can be translated to express
a luciferase reporter gene, implicating RNA polymerase II. TATA mutations
that disrupt TATA-binding protein (TBP) interactions inhibit +29
transcription and luciferase expression. Co-expressed TBP proteins bearing
compensatory mutations restore +29 transcription and luciferase activity,
suggesting a direct TBP-TATA interaction. Importantly, +1 transcription is
unaffected by the TATA mutations, suggesting that in the context of pol I
recognition, the TATA-containing initiator element serves a function other
than TBP binding.
ARTICLES
Species-specificity of rRNA gene transcription in plants manifested as a switch in RNA polymerase specificity
Biology Department, Washington University, St Louis, MO 63130, USA.
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