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Circularization of Tn 916 is required for expression of the transposon‐encoded transfer functions: characterization of long tetracycline‐inducible transcripts reading through the attachment site
Author(s) -
Celli Jean,
TrieuCuot Patrick
Publication year - 1998
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 - 10.1046/j.1365-2958.1998.00778.x
Subject(s) - biology , transposable element , gene , transcription (linguistics) , genetics , homology (biology) , repressor , promoter , microbiology and biotechnology , gene expression , mutant , linguistics , philosophy
A detailed transcriptional analysis of the conjugative transposon Tn 916 was carried out, which revealed that transcription of the transfer functions requires excision of the element and dramatically increases in the presence of tetracycline. The key components of this regulatory system are two contiguous transposon‐borne genes, orf7 and orf8 , located downstream from and having the same polarity of transcription as the tetracycline resistance determinant tetM . The gene orf7 encodes a 140‐amino‐acid (aa) protein exhibiting limited homology with σ F of Bacillus subtilis , whereas orf8 encodes a 76‐aa peptide that does not share any sequence homology with any cognate proteins. In the presence of tetracycline, an attenuation mechanism enables the transcription of orf7 and orf8 from the tetM promoter. The resulting increased synthesis of ORF7 and ORF8 activates the promoter P orf7 located upstream from orf7 , which then directs the expression of the transfer functions in the transposon circular intermediate through long transcripts encompassing the attachment site. The apparently non‐regulated promoter P xis located upstream of the excisionase encoding gene xis could also participate in the expression of the tra genes. We also demonstrate that Tn 916 carries another regulated promoter, P orf9 , which directs transcription of a single gene, orf9 , located downstream from and transcribed counterclockwise to tetM . This gene encodes a 117‐aa putative transcriptional repressor, but the exact role of this protein in the mobility of Tn 916 , as well as the regulation of its expression, remains to be elucidated. Our results constitute the molecular basis for the observation that tetracycline increased the transfer frequency of this type of element.