Atypical Polycomb group protein, which may be involved in both Polycomb group (PcG) and trithorax group (trxG) complexes. Non-catalytic component of the PR-DUB complex, a complex that specifically mediates deubiquitination of histone H2A monoubiquitinated at 'Lys-118' (H2AK118ub1). Does not deubiquitinate monoubiquitinated histone H2B. Required to maintain the transcriptionally repressive state of homeotic genes throughout development. The PR-DUB complex has weak or no activity toward 'Lys-48'- and 'Lys-63'-linked polyubiquitin chains. PcG and trxG proteins act by forming multiprotein complexes, which are respectively required to maintain the transcriptionally repressive and transcriptionally active state of homeotic genes throughout development. PcG and trxG protein complexes are not required to initiate repression and activation, but to maintain it during later stages of development. Component of the PR-DUB complex, at least composed of calypso and Asx (PubMed:20436459). Interacts with tant (PubMed:11397012). Interacts with cyclin CycG (PubMed:25995770). Associated with chromatin. Colocalizes with many PcG sites on polytene chromosomes. It also associates with many unique sites on polytene chromosomes. Highly expressed in nurse cells and deposited in oocytes late in oogenesis. Ubiquitous in early embryos. Late embryos show higher levels in CNS and neurectoderm. Expressed both maternally and zygotically. Early embryos have high levels of expression, this drops off and zygotic expression begins at 3-6 hours embryos. Expression levels are low in larvae and medium in pupae and adults. Contains two Leu-Xaa-Xaa-Leu-Leu (LXXLL) motifs, which may be required for an association with nuclear receptors. Belongs to the Asx family.