On the cover: Numb is a conserved endocytic adaptor protein involved in numerous cellular functions. Mass spectrometry analysis revealed both novel and known associations of Numb with proteins involved in both intracellular transport and signal transduction. Targeted SRM-MS was used to show the preferential association between interacting proteins and Numb isoforms, as well as to monitor the endocytic mediated dynamic regulation of these interactions. For details, see the article by Jonathan R. Krieger, et al., pages 499–514