RNA-Protein Reciprocity and the Limits of RBP Buffering.

RNA-binding proteins (RBPs) regulate RNA processing, localization, translation, and decay, yet similar perturbations can have different consequences across cells and tissues. RNA-protein reciprocity relates this variation to the balance between the binding sites presented by RNA and the protein available to regulate them. Regulation can remain stable while sufficient RBP is available, but become sensitive to small changes as that reserve narrows. The biological consequence depends on which transcripts lose regulation and how strongly the cell depends on their products. Examples from endogenous regulatory RNAs, repeat-expansion diseases, viral infection, and cancer show that RNA-dependent RBP redistribution can preserve cellular function or contribute to its failure. Binding affinity, partner proteins, autoregulation, and RNA-dependent assembly shape these responses. This Perspective develops the framework and proposes experiments to connect changes in local RNA demand and RBP supply with target binding and biological output. The aim is to identify when a modest molecular perturbation has a disproportionate functional effect, and when restoring the RNA-protein balance can recover regulation.