https://www.selleckchem.com/products/pd-1-pd-l1-inhibitor-1.html Understanding protein-protein interactions is key to unraveling protein function in vivo. Here we describe a dual/triple-plasmid system that enables co-expression of two, or three, recombinant proteins harboring different affinity tags in the same Escherichia coli cell. This novel protein expression system provides a platform to understand protein-protein interactions and enables researchers to study protein complex formation and in vivo localization.Single-stranded DNA (ssDNA)-binding protein (SSB) is essential for DNA metabolic processes. SSB also binds to many DNA-binding proteins that constitute the SSB interactome. The mechanism through which PriA helicase, an initiator protein in the DNA replication restart process, is stimulated by SSB in Escherichia coli (EcSSB) has been established. However, some Gram-positive bacterial SSBs such as Bacillus subtilis SsbA (a counterpart of EcSSB), Staphylococcus aureus SsbA, SsbB, and SsbC do not activate PriA helicase. Here, we describe some of the methods used in our laboratory to compare SSB-PriA functional and physical interactions in Gram-positive and -negative bacteria.Recent single-molecule studies have demonstrated that the composition of multi-protein complexes can strike a balance between stability and dynamics. Proteins can dynamically exchange in and out of the complex depending on their concentration in solution. These exchange dynamics are a key determinant of the molecular pathways available to multi-protein complexes. It is therefore important that we develop robust and reproducible assays to study protein exchange. Using DNA replication as an example, we describe three single-molecule fluorescence assays used to study protein exchange dynamics. In the chase exchange assay, fluorescently labeled proteins are challenged by unlabeled proteins, where exchange results in the disappearance of the fluorescence signal. In the FRAP exchange assay, fluo