PIR, also known as pirin, is a member of the cupin superfamily. PIR is an Fe(II)-containing nuclear protein expressed in all tissues of the body and concentrated within dot-like subnuclear structures. Interactions with nuclear factor I/CCAAT box transcription factor as well as B cell lymphoma 3-encoded oncoprotein suggest the encoded protein may act as a transcriptional cofactor and be involved in the regulation of DNA transcription and replication.