Circularization of Tn916 is required for expression of the transposon‐encoded transfer functions: characterization of long tetracycline‐inducible transcripts reading through the attachment site

Abstract

SummaryA detailed transcriptional analysis of the conjugative transposon Tn916 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 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 Tn916 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 Tn916, 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.

Characterization of Genes Involved in Modulation of Conjugal Transfer of theBacteroidesConjugative Transposon CTnDOT

“…The gram-positive CTn Tn916 solves this coordination problem structurally, since excision and circularization of the transfer intermediate are required for the expression of transposonencoded transfer functions (5). In Tn916, the expression of tra functions in the circular intermediate is due to transcription from a promoter that runs through the attachment site.…”

Antimicrobial Resistance and Potential Probiotic Application of Enterococcus spp. in Sea Bass and Sea Bream Aquaculture

“…The molecular details of the structures and functions of these elements are fairly well studied and becoming understood (Clewell et al, 1995;Marra & Scott 1999). It is noteworthy that transcription of the transfer functions of Tn916 requiring excission of the element is dramatically increased in the presence of tetracyclin (Celli & Trieu-Cuot 1998).…”

Tales of conjugation and sex pheromones

“…103 (10) Celli and Triu-Cuot have reported that exposure to tetracycline results in transcription that extends beyond tet and can indirectly enhance transcription of xis and int. 104 If excision has occurred, transcription can proceed across the junction sequence into the similarly oriented conjugation determinants thereby upregulating conjugative transfer.…”