Transcriptional organization of the temperature-sensitive transfer system from the IncHI1 plasmid R27.
One of the characteristic features of IncHI1 plasmids is a thermosensitive process of conjugation, which is optimal between 22 degrees C and 30 degrees C but inhibited at 37 degrees C. R27, the prototypical IncHI1 plasmid, contains transfer genes clustered in two regions of the plasmid, Tra1 and Tra2. In the present study, transcriptional analyses of the tra genes were undertaken at both 30 degrees C and 37 degrees C. Screening of 38 tra genes showed that tra genes are transcriptionally linked in six operons, three in each Tra region. RT-PCR analysis showed that gene expression was reduced at 37 degrees C relative to that observed at 30 degrees C. The transcription start sites of the six transcripts were identified, promoters and upstream regions were cloned, and transcription was tested at both temperatures. In cells grown at 37 degrees C, in the presence of R27, the promoters were inhibited, except for promoters of the H operon and AN operon. Conditions that influenced DNA topology, such as osmolarity, anaerobiosis, quorum sensing and acidity, showed no significant influence on transfer frequency. These results should facilitate future understanding of the basis of temperature-sensitive transfer in this large conjugative plasmid.
Alonso
Guillermina
G
Instituto de Biología Experimental, Facultad de Ciencias, Universidad Central de Venezuela. Caracas, Venezuela.
Baptista
Kelly
K
Department of Medical Microbiology and Immunology, 1-63 Medical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Ngo
Trinh
T
Department of Medical Microbiology and Immunology, 1-63 Medical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Taylor
Diane E
DE
Department of Medical Microbiology and Immunology, 1-63 Medical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
D001426:Bacterial Proteins; D001483:Base Sequence; D003227:Conjugation, Genetic; D004268:DNA-Binding Proteins; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D022761:Gene Transfer, Horizontal; D008969:Molecular Sequence Data; D009876:Operon; D011401:Promoter Regions, Genetic; D011815:R Factors / Q000235:genetics*; D013696:Temperature; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria