Fluorescent proteins have become a useful and ubiquitous tool for making chimeric proteins, where they function as a fluorescent protein tag. Typically they tolerate N- and C-terminal fusion to a broad variety of proteins. They have been expressed in most known cell types and are used as a noninvasive fluorescent marker in living cells and organisms. They enable a wide range of applications where they have functioned as a cell lineage tracer, reporter of gene expression, or as a measure of protein-protein interactions.Red Fluorescent Protein (RFP) is a versatile biological marker for monitoring physiological processes, visualizing protein localization, and detecting transgenic expression in vivo. RFP can be excited by the 488 nm or 532 nm laser line and is optimally detected at 588 nm.