Figure 1. Fluorescent Timer lets you visualize changes in promoter activity. A transgenic C. elegans embryo containing Fluorescent Timer fused to the heat shock promoter hsp16-41 was heat-shocked by flotation in a 33°C water bath. Promoter activity was studied during the heat shock recovery period. Images were taken with a Chroma Polycroich beam-splitter 86100bs filter set and analyzed with MetaMorph Software. If both green and red fluores-cence are present, the two colors together appear yellow in an overlay.