Core component of the TRAPP complexes which has a function of guanine nucleotide exchange factor activity for Rab1 GTPase (Probable). Plays a role in vesicular transport from endoplasmic reticulum to Golgi and autophagy (PubMed:31794024). May play a role in dendrite postsynaptic membrane trafficking (By similarity). {ECO:0000250|UniProtKB:Q9ES56, ECO:0000269|PubMed:31794024, ECO:0000305|PubMed:31794024}. This is the function of Ensembl gene identifier ENSG00000196655 (TRAPPC4, trafficking protein particle complex subunit 4).