LOV Domains as In Vivo Fluorescent Reporters of Protein Expression

Chromophore-binding domains from plant and bacterial photoreceptors have received increasing interest as new sources of genetically encoded fluorescent proteins (FPs). In particular, FPs based on the flavin-binding LOV (Light, Oxygen, or Voltage sensing) domain offer advantages over green fluorescent protein (GFP) owing to their smaller size and utility under anaerobic conditions. Recombinant expression of LOV domains in Escherichia coli (E. coli) is fast, easy to detect, and inexpensive given the innate ability of LOV domains to acquire their ubiquitous organic cofactor from the cellular environment. This manuscript describes the strategies and variables to consider when expressing and purifying LOV-domain protein fusions from liquid cultures of E. coli. Strategies for expressing and visualizing LOV-domain fusion proteins in E. coli grown on agar medium are also described. Curr. Protoc. Essential Lab. Tech. 6:13.1.1-13.1.11. © 2012 by John Wiley & Sons, Inc.