Regulatory subunit of the IKK core complex which phosphorylates inhibitors of NF-kappa-B thus leading to the dissociation of the inhibitor/NF-kappa-B complex and ultimately the degradation of the inhibitor (PubMed:14695475, PubMed:20724660, PubMed:21518757, PubMed:9751060). Its binding to scaffolding polyubiquitin plays a key role in IKK activation by multiple signaling receptor pathways (PubMed:16547522, PubMed:18287044, PubMed:19033441, PubMed:19185524, PubMed:21606507, PubMed:27777308, PubMed:33567255). Can recognize and bind both 'Lys-63'-linked and linear polyubiquitin upon cell stimulation, with a much higher affinity for linear polyubiquitin (PubMed:16547522, PubMed:18287044, PubMed:19033441, PubMed:19185524, PubMed:21606507, PubMed:27777308). Could be implicated in NF-kappa-B-mediated protection from cytokine toxicity. Essential for viral activation of IRF3 (PubMed:19854139). Involved in TLR3- and IFIH1-mediated antiviral innate response; this function requires 'Lys- 27'-linked polyubiquitination (PubMed:20724660). {ECO:0000269|PubMed:14695475, ECO:0000269|PubMed:16547522, ECO:0000269|PubMed:18287044, ECO:0000269|PubMed:19033441, ECO:0000269|PubMed:19185524, ECO:0000269|PubMed:19854139, ECO:0000269|PubMed:20724660, ECO:0000269|PubMed:21518757, ECO:0000269|PubMed:21606507, ECO:0000269|PubMed:27777308, ECO:0000269|PubMed:33567255, ECO:0000269|PubMed:9751060}. (Microbial infection) Also considered to be a mediator for HTLV-1 Tax oncoprotein activation of NF-kappa-B. . This is the function of IKBKG (inhibitor of nuclear factor kappa B kinase regulatory subunit gamma, ENSG00000269335).