Abstract
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.
Highlights
The central step in regulation of gene expression is the transcription process
Promoter strength was measured in terms of -galactosidase activity of the wild type mom and spacer mutant promoters in the absence and presence of C protein (Table I)
We have addressed the mechanism of C-mediated transactivation of the mom gene of bacteriophage Mu [15]
Summary
The central step in regulation of gene expression is the transcription process. In prokaryotes, the transcriptional apparatus consists of the RNA polymerase, the various regulators (activators and repressors), and the promoter region. 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.
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