DNA Unwinding Mechanism for the Transcriptional Activation of
momP1 Promoter by the Transactivator Protein C of
Bacteriophage Mu*
Shashwati
Basak
§ and
Valakunja
Nagaraja
¶
From the
Department of Microbiology and Cell Biology,
Indian Institute of Science, Bangalore 560 012, India and the
¶ Jawaharlal Nehru Centre for Advanced Scientific Research,
Bangalore 560 064, India
Transcription factor-induced conformational
changes in DNA are one of the mechanisms of transcription activation. C
protein of bacteriophage Mu appears to transactivate the
mom gene of the phage by this mode. DNA binding by C to its
site leads to torsional changes that seem to compensate for a weak
momP1 promoter having a suboptimal spacing of 19 bp between
the poor
35 and
10 elements. The C-mediated unwinding could realign
the promoter elements for RNA polymerase recruitment to the reoriented
promoter. In this study, the model has been tested by mutational
analysis of the spacer region of momP1 and by assessing the
strength of the mutant promoters. The response to C-mediated
transactivation was dependent on the spacer length of the promoters.
Mutants with 17-bp spacing between the two promoter elements showed
reduced activity in the presence of the transactivator as compared with
their basal level. A synthetic promoter with near consensus promoter
elements and optimal 17-bp spacing was also tested to evaluate the
model. The results imply a role for C-mediated unwinding in
mom transcription activation.
*
This work was supported by a grant from the Department of
Science and Technology, Government of India (to V. N.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
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accordance with 18 U.S.C. Section
1734 solely to indicate this fact.