The function of RNF39 (ring finger protein 39, ENSG00000204618) is as follows. Plays an inhibitory role in anti-RNA viral innate immunity by targeting the adapter DDX3X and promoting its 'Lys-48'-linked polyubiquitination (PubMed:33674311). Alternatively, enhances the cGAS- STING pathway activation by promoting 'Lys-63'-linked ubiquitination of STING1, facilitating the STING1-TBK1 complex formation and STING1 activation (PubMed:39255680). {ECO:0000269|PubMed:33674311, ECO:0000269|PubMed:39255680}. (Microbial infection) Plays a positive role in human immunodeficiency virus (HIV-1) replication. .