APAP-1, also known as AAP1 and RYBP, is widely expressed. It is highest expressed in lymphoid tissues and placenta. APAP-1 contains 1 RanBP2-type zinc finger. It may bind to DNA. APAP-1 inhibits ubiquitination and subsequent degradation of TP53, and thereby plays a role in regulating transcription of TP53 target genes. It may be implicated in the regulation of the transcription as a repressor of the transcriptional activity of E4TF1. APAP-1 also promotes apoptosis.