Protein-protein interactions (PPIs) are of fundamental importance in several cellular processes. While “classical” biochemical methods are commonly used to monitor protein multimerization in biological samples, fluorescence microscopy offers the possibility to investigate PPIs directly in living cells, even distinguishing among different cellular compartments. In this chapter, we shortly describe the most common procedures used to label proteins with fluorescent probes. Furthermore, we discuss a variety of fluorescence microscopy techniques that can be used to obtain quantitative information about protein multimerization. Special emphasis is given to fluorescence fluctuation techniques and their applications in the context of, e.g., receptor multimerization and virus assembly.

蛋白质-蛋白质相互作用（PPI）在几种细胞过程中至关重要。尽管通常使用“经典”生化方法来监测生物样品中的蛋白质多聚化，但荧光显微镜提供了直接研究活细胞中PPI的可能性，甚至可以区分不同的细胞区室。在本章中，我们简要介绍了使用荧光探针标记蛋白质的最常用方法。此外，我们讨论了各种荧光显微镜技术，可用于获取有关蛋白质多聚化的定量信息。特别强调了荧光波动技术及其在例如受体多聚化和病毒组装中的应用。