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An adaptor protein connects other components of a molecular pathway through binding interactions. Multiple interaction domains can bring a receptor, an enzyme and a cytoskeletal partner into one local assembly. The adaptor need not itself catalyse the pathway’s chemical reaction. Its abundance and localization can still regulate signalling by changing which partners encounter one another. Nck illustrates an adaptor linking phosphorylation-dependent recognition to downstream assemblies. ^[ref]

UPF2 is an adaptor protein in nonsense-mediated decay that interacts with UPF1 and UPF3. These interactions help couple the context of an RNA-protein assembly to activation of the decay pathway. The role is regulatory and organizational rather than simply recognizing a particular three-base stop codon in isolation. Different substrates can depend differently on individual surveillance components. ^[ref]