Transcription factor induced conformational changes in DNA is one of the mechanisms of transcription activation. C protein of bacteriophage Mu appears to transactivate '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 assessing 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 presence of the transactivator as compared to 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.