A reporter gene GUS (uid A) is a fusion protein used to study the expression pattern of transgenic plants. A gene fusion is a DNA structure (in vitro or in vivo) in which the regulatory sequences of one gene influence the transcription and/or translation of the coding sequences of another gene (a reporter). This histochemical assay is used to investigate the mechanism of plant transformation events, cellular expressions, function of the plant genome, and their level of expression in genes.