Nucleic Acids Research, 1988, Vol. 16, No. 12 5277-5290
© 1988
Articles |
A second RNA-polymerase can bind specifically to the bla promoter of Tn3, repressing transcription initiation
Institut Jacques Monod, Centre National de la Recherche Scientifique and Université de Paris VII 2 place Jussieu, tour 43, 75251 Paris, Cedex 05, France
To whom correspondence should be addressed
Received April 12, 1988. Revised May 16, 1988. Accepted May 16, 1988.
We showed earlier [10] that the region of the bla promoter of Tn3 protected by the RNA-polymerase (RNAP), has the normal size (about 60bp) at RNAP/promotar molar ratio r(2, but rises to about twice this extent as r increases. We confirm here that the species corresponding to normal and extended footprint distinguish by their electrophoretic mobilities. Furthermore, inspection of the complexes by electron microscopy confirms that at r>2, the bla promoter can bind specifically a second RNAP particle, as compared to the 1:1 complex observed at r(2. At r>2, the ability of the bla promoter to initiate transcription in vitro is repressed when compared to the complex 1:1 obtained at r>2. The unexpected decrease in initiation efficiency as the concentration of RNAP particles is increased, together with the striking sequence homology of the bla promoter with promoters of stable RNA, suggest that in vivo, this promoter could be regulated by growth rate.
1Present address: Instituto de Investigaciones Biologicas Clemente Estable, Avda. Italia, 3318 Montevideo and Facultad de Humanidades y Ciencias, Tristan Narvaja, 1674 Montevideo, Uruguay