Enables NF-kappaB binding activity. Involved in T cell receptor signaling pathway and positive regulation of T-helper 17 cell differentiation. Acts upstream of or within several processes, including negative regulation of NF-kappaB transcription factor activity; negative regulation of T cell differentiation in thymus; and positive regulation of thymocyte apoptotic process. Located in nucleus. Orthologous to human NFKBID (NFKB inhibitor delta). [provided by Alliance of Genome Resources, Apr 2022]