When Bacillus subtilis is grown in the presence of excess tryptophan, transcription of the trp operon is regulated by binding of tryptophan-activated TRAP to trp leader RNA, which promotes transcription termination in the trp leader region. Transcriptome analysis of a B. subtilis strain lacking polynucleotide phosphorylase (PNPase; a 3′-to-5′ exoribonuclease) revealed a striking overexpression of trp operon structural genes when the strain was grown in the presence of abundant tryptophan. Analysis of trp leader RNA in the PNPase- strain showed accumulation of a stable, TRAP-protected fragment of trp leader RNA. Loss of trp operon transcriptional regulation in the PNPase- strain was due to the inability of ribonucleases other than PNPase to degrade TRAP-bound leader RNA, resulting in the sequestration of limiting TRAP. Thus, in the case of the B. subtilis trp operon, specific ribonuclease degradation of RNA in an RNA-protein complex is required for recycling of an RNA-binding protein. Such a mechanism may be relevant to other systems in which limiting concentrations of an RNA-binding protein must keep pace with ongoing transcription.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Mar 2 2004|
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