Negatively regulates endocytic trafficking. Impairs the autophagosome maturation process. May inhibit PIK3C3 activity. Forms a complex with BECN1, PIK3C3, PIK3R4 and UVRAG, but not with ATG14. The complex containing ATG14 up-regulates autophagy, while the one containing Rubicon down-regulates autophagy. 3 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.