In vrvo footprintmg is a method of observmg DNA/protein mteractions of a gene within the context of the livmg cell. In other words, in vivo footprintmg provides an opportunity to observe conformational changes in chromatm associated with the transcriptional machinery of a cell as it responds to environmental and developmental signals in viva. The DNA/protein interactions targeted by m viva footprintmg can be visualized through the use of genomic sequencing, a technique that can provide strand-specific resolution of single bases (1 ).