In vitro transcription of plant RNA polymerase I-dependent rRNA genes is species-specific.

An in vitro transcription system derived from tobacco (Nicotiana tabacum) cultured cell (BY-2) nuclei supports transcription of the RNA polymerase I-dependent tobacco rRNA gene. The transcription initiation site determined in vitro was found at residue A which corresponds to that lying within the consensus sequence surrounding plant pre-rRNA initiation sites. The tobacco rRNA gene is actively transcribed in the tobacco nuclear extract while the broad bean rRNA gene is inactive in the heterologous system, indicating that plant RNA polymerase I-dependent transcription is species-specific.