Dual role for transactivator protein C in activation of mom promoter of bacteriophage Mu

doi:10.1074/jbc.M512906200

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Papers In Press, published online ahead of print January 30, 2006
J. Biol. Chem, 10.1074/jbc.M512906200
Submitted on December 2, 2005
Revised on January 18, 2006
Accepted on January 30, 2006

Dual role for transactivator protein C in activation of mom promoter of bacteriophage Mu

Atanu Chakraborty and Valakunja Nagaraja

Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, Karnataka 560012

Corresponding Author: vraj{at}mcbl.iisc.ernet.in

Transactivator C protein of bacteriophage Mu activates mom gene of the phage by an unusual mechanism. DNA binding by C to its site results in unwinding of the neighboring sequences, realigning the out of phase promoter elements to facilitate RNA polymerase (RNAP) binding. High-level stimulation of a C independent constitutive promoter mutant, where RNAP is already bound, by the transactivator suggested additional mechanism of transcription activation at a step after RNAP recruitment. In this study, we have investigated the various steps of promoter-polymerase interactions during transcription initiation by using both the promoter mutant and a positive control (pc) mutant of C protein. The transactivator does not influence formation of open complex or its stability after facilitating the RNAP binding. However, at a subsequent step, the protein exerts an important role, enhancing the promoter clearance by increasing the productive RNAP-promoter complex. The pc mutant of the transactivator C is compromised at this step, supporting the additional downstream role for C in mom transcription activation. We suggest that this unusual multi-step activation of Pmom has evolved to ensure irreversibility of the switch during late lytic cycle of the phage.

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