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Intracistronic transcriptional polarity enhances translational repression: a new role for Rho
Author(s) -
De Smit Maarten H.,
Verlaan Paul W. G.,
Van Duin Jan,
Pleij Cornelis W. A.
Publication year - 2008
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2008.06360.x
Subject(s) - biology , terminator (solar) , ribosome , microbiology and biotechnology , psychological repression , translation (biology) , post transcriptional regulation , translational regulation , transcriptional regulation , regulation of gene expression , operon , cistron , gene expression , transcription (linguistics) , messenger rna , rna , gene , genetics , escherichia coli , ionosphere , linguistics , physics , philosophy , astronomy
Summary Transcriptional polarity in Escherichia coli occurs when cryptic Rho‐dependent transcription terminators become activated as a consequence of reduced translation. Whether this is due to an increased spacing between the RNA polymerase and the leading ribosome or to prior functional inactivation of a subpopulation of the mRNAs has been a matter of discussion. Transcriptional polarity results in decreased synthesis of inefficiently translated mRNAs and therefore in decreased expression of downstream genes in the same operon ( inter cistronic polarity). By analogy, expression of the gene in which the conditional termination occurs is also expected to decrease, but this has so far not been demonstrated experimentally. To study the relevance of this intra cistronic polarity for expression regulation in vivo , the polarity‐prone lacZ reporter gene was fused to a range of mutated ribosome binding sites, repressed to different degrees by local RNA structure. Quantitative analysis of protein and mRNA synthesis shows that polarity occurs on functionally active mRNA molecules and that it indeed affects expression of the cistron carrying the terminator, thus enhancing the effect of translational repression. These findings point to a novel regulatory function of transcriptional polarity, reminiscent of transcriptional attenuation but opposite in effect.