The present invention describes the identification, isolation and characterization of novel mammalian proteins encoded by the Ese1 and Ese2 genes which are involved in endocytosis, vesicular trafficking and regulation of the actin cytoskeleton. Transcripts and products of these genes are useful for detecting abnormal cellular endocytosis processes as well as for developing assay systems to find and elucidate further binding partners of the proteins, to develop therapeutics to alter/restore protein function and for the isolation and manufacture of Ese proteins.