Through the activation of JUN and AP-1-mediated transcription, may regulate apoptosis. Interacts with COPS5; regulates the phosphorylation of JUN and the transcriptional activity of AP-1. Interacts with RYBP; may prevent the ubiquitin-mediated proteasomal degradation of FANK1. Weakly detected in the cytoplasm of elongated spermatids. Mostly restricted to testis (at protein level), including mid to late pachytene spermatocytes (stages VI-X), diplotene spermatocytes (stage XI), meiotically dividing spermatocytes (stage XII) and spermatids in steps 1-14. Highest levels in late pachytene spermatocytes and spermatids in steps 1-9. In the developing testis, first detected at postnatal day 14 (P14) and levels increase after P20 (at protein level). At P20, detected in pachytene spermatocytes and round spermatids, but not in preleptotene and leptotene spermatocytes. Not detected in testis at P10. Detected in germinal vesicle (GV) stage oocytes and in embryos up to the 2-cell stage, but not in morula or blastocysts. Expression is activated by FOXJ1. The fibronectin type-III domain mediates interaction with COPS5 and RYBP. Polyubiquitinated. Polyubiquitination leads to proteasomal degradation.