RAB5A effector molecule that is involved in vesicular trafficking of early endosomes. Mediates the recruitment of HTT by RAB5A onto early endosomes. 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. Interacts with HTT (via C-terminus) (PubMed:16476778). Interacts with RAB5A (PubMed:16476778). Found in a complex with F8A1/F8A2/F8A3, HTT and RAB5A; mediates the recruitment of HTT by RAB5A onto early endosomes (PubMed:16476778). Diffuse presence in the cytoplasm and accumulation in the nucleus (By similarity). In absence of HTT, F8A1/F8A2/F8A3 is concentred in cytoplasm (By similarity). 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 (By similarity).