Transcription factors (TFs) are a group of cellular proteins that play essential roles in regulating gene expression. They act as a sensor to monitor cellular change and convert the signals into gene expression. A specific TF is often regulated by multiple upstream proteins. Monitoring the activation of a TF is critical to uncovering the mechanism of signal pathways and cellular regulations. Signosis developed 48 different filter assays for monitoring the activities of TFs. Unlike gel shift assays, 96 samples can be analyzed in one experiment.