Observables for seperating droplets and binding-site clusers in foci

The spatial organization of complex biochemical reactions is of fundamental importance in order to maintain correct regulation of cellular processes. Small structures known as foci create local high concentrations of proteins needed for DNA repair. One specific way to introduce such a heterogeneity is by the process of a phase separation where proteins with energetically favorable interactions cluster inside droplets. However it is still extremely difficult to define whether observable foci are formed as a phase separation or merely as the result of an increased number of specific binding sites. In this work we outline possible observables to differentiate between the two existing models based on tracking of single molecules. We discuss relations between the steady state behaviour and the diffusion properties on shorter time scales as a way to identify the underlying physical structure of foci.