Fluorescence co-localization is the analysis of the position where the signals of two fluorescent labels are co-distributed in the sample, usually in two ways: "gene-tag" fusion protein expression and immunofluorescence. Colocalization, as it literally means, can show that both protein A and B are expressed in this cell, and they are in the same intracellular location, which is the cytological evidence of the direct or indirect interaction between the two proteins. This technique is generally used to assist in the identification of protein interactions in cells, and can be used as an auxiliary detection method for other protein interaction research methods.