Transcriptional regulator that acts as a repressor or an activator. Acts as a transcriptional repressor on minimal promoter containing mu E3 enhancer sequence. Binds to mu E3 DNA sequence of the immunoglobulin heavy-chain gene enhancer. Acts as a transcriptional transactivator on the proximal promoter region of the tartrate-resistant acid phosphatase (TRAP) E-box containing promoter (By similarity). Collaborates with MITF in target gene activation (By similarity). Acts as a transcriptional repressor on minimal promoter containing mu E3 enhancer sequence (By similarity). Binds to mu E3 DNA sequence of the immunoglobulin heavy-chain gene enhancer (By similarity). Binds DNA in a homo- or heterodimeric form. Homodimer. Forms heterodimers with TFE3. Forms heterodimers with MITF (By similarity). Interacts with MITF (By similarity). Expressed in kidney, spleen, lung, liver, testis and muscle. Expressed in embryo at 14 dpc and in skeletal muscle at 18 dpc. Belongs to the MiT/TFE family. Extended N-terminus. Truncated C-terminus.