RAB5A effector molecule that is involved in vesicular trafficking of early endosomes. Mediates the recruitment of HTT by RAB5A onto early endosomes (By similarity). The HTT-F8A1/F8A2/F8A3-RAB5A complex stimulates early endosomal interaction with actin filaments and inhibits interaction with microtubules, leading to the reduction of endosome motility (PubMed:16476778). Interacts with HTT (via C-terminus) (PubMed:11035034). Interacts with RAB5A (By similarity). Found in a complex with F8A1/F8A2/F8A3, HTT and RAB5A; mediates the recruitment of HTT by RAB5A onto early endosomes (By similarity). Diffuse presence in the cytoplasm and accumulation in the nucleus (By similarity). In absence of HTT, F8A1/F8A2/F8A3 is concentred in cytoplasm (PubMed:11035034). Colocalized with HTT in endosomes (By similarity). In neuron found in intranuclear structures, the intranuclear rodlets (INRs), also known as rodlets of Roncoroni, in association with ubiquitin (PubMed:23749422). Produced abundantly in a wide variety of cell types.