What do colocalization studies demonstrate?

Colocalization studies are primarily used to investigate the cellular localization of two proteins within a particular cellular context. By tagging or labeling the proteins of interest with different fluorescent markers and using imaging techniques such as confocal microscopy, researchers can visualize the locations of these proteins simultaneously in intact cells. If the fluorescent signals overlap or are found within the same cellular compartment, it indicates that the two proteins are present in the same region of the cell.

This technique does not directly provide evidence of interaction, which would require additional assays such as co-immunoprecipitation or FRET (Förster Resonance Energy Transfer). It also does not involve determining the presence of antibodies in solution or measuring distances between cellular compartments, as those are focused on different aspects of biochemical research. Therefore, the core contribution of colocalization studies lies in establishing where proteins are located within the cell, making option B the most accurate description of what colocalization studies demonstrate.