Enables leptomycin B binding activity; protein domain specific binding activity; and transcription regulator inhibitor activity. Involved in negative regulation of myoblast differentiation; negative regulation of transcription, DNA-templated; and positive regulation of gene expression. Acts upstream of or within several processes, including animal organ development; cellular response to leptomycin B; and negative regulation of macromolecule metabolic process. Located in cytoplasm and nucleus. Is expressed in several structures, including alimentary system; central nervous system; limb; metanephros; and sensory organ. Used to study Sjogren's syndrome. Orthologous to human ID3 (inhibitor of DNA binding 3, HLH protein). [provided by Alliance of Genome Resources, Apr 2022]