Premium
Regulatory mechanisms in expression of the traY‐I operon of sex factor plasmid R100: involvement of traJ and traY gene products
Author(s) -
Taki Keiko,
Abo Tatsuhiko,
Ohtsubo Eiichi
Publication year - 1998
Publication title -
genes to cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.912
H-Index - 115
eISSN - 1365-2443
pISSN - 1356-9597
DOI - 10.1046/j.1365-2443.1998.00194.x
Subject(s) - operon , biology , plasmid , gene , tray , genetics , microbiology and biotechnology , escherichia coli , botany
Background : The plasmid R100 encodes tra genes essential for conjugal DNA transfer in Escherichia coli . Genetic evidence suggests that the traJ gene encodes a positive regulator for the traY‐I operon, which includes almost all the tra genes located downstream of traJ . The molecular mechanism of regulation by TraJ, however, is not yet understood. traY is the most proximal gene in the traY‐I operon. TraY promotes DNA transfer by binding to a site, sbyA , near the origin of transfer. TraY is suggested to have another role in regulation of the traY‐I operon, since it binds to two other sites, named sbyB and sbyC , located in the region preceding traY‐I .Results : Using a traY‐lacZ fusion gene, we showed that the traY‐I operon was expressed only in the presence of traJ . The TraJ‐dependent expression of traY‐I required the E. coli arcA gene, which encodes a host factor required for conjugation. TraJ‐dependent transcription occurred from a promoter (named p Y) located upstream of traY‐I . The isolated TraJ protein was found to bind to a dyad symmetry sequence, named sbj (specific binding site of TraJ), which existed in the intergenic region between traJ and traY‐I . We also demonstrated that TraY repressed the TraJ‐dependent expression of traY‐I at the TraY binding sites, sbyB and sbyC , which overlapped with p Y.Conclusions : TraJ is a protein which binds to the sbj site in the region upstream of the promoter p Y and positively regulates expression of the traY‐I operon in the presence of the E. coli arcA gene. Since sbj is located 93 bp upstream of p Y in the intergenic region between traJ and traY‐I , TraJ presumably contacts with a transcription apparatus to promote transcription from p Y. TraY, which is known to activate the initiation of conjugal DNA transfer, has a new role in the transcriptional autoregulation of traY‐I expression. At levels which are sufficient to initiate conjugal DNA transfer, TraY represses traY‐I transcription in the presence of TraJ.