Nucleic Acids Research, 1988, Vol. 16, No. 5 2031-2044
© 1988
Articles |
Far upstream sequences of the bla promoter from TN3 are involved in complexation with E.coli RNA-polymerase
Institut Jacques Monod, Centre National de Ia Recherche Scientifique and Université de Paris VII 2, place Jussieu Tour 43, 75251 Paris Cedex 05, France
*To whom correspondence should be addressed
Received November 25, 1987. Revised February 10, 1988. Accepted February 10, 1988.
The structure of the final initiation complex between E.coli RH polymerase (RNAP) and the bla promoter from the transposon TN3 has been probed by footprinting experiments and base accessibility to dimethyl sulfate at 37°C. At RNAP/promoter molar ratios "standard" for these experiments 10), the contacts on bla extend from –100 to +20, i.e. a length exceding twice the dimension of the RNAP major axis [33]. Since footprinting at about equimolar asounts of RNAP and bla extends to the usual (–55 to +20) promoter domain, it is very likely that at least two RNAP's participate in the complex observed at tenfold higher RNAP/bla ratios. Under the latter conditions, the extended footprint (–100 to +20) is observed above 30°C whereas at 15°C only the –55 to +20 promoter area is contacted. Furthermore, gel retardation experiments show the presence of two complexes of different migration rates. Ye have reported earlier [21] that at the "standard" RNAP/bla ratio, transcription initiation from the bla promoter is inhibited. The correlation of this inhibition with the postulated two RNAP/bla complex suggests a regulation of bla gene expression by RNAP avaibility controlled for instance by growth rate. These results can be correlated with those reported in [14, 15] for the tyrT promoter. Interestingly, both promoter share significant sequence homologies.
1On leave of absence. Present address: Instituto de Investigaciones Biologicas Clemente Estable, Avda. Italia 3318 and Facultad de Humanidades y Ciencias, Tristan Narvaja 1674, Montevideo, Uruguay
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