Involved in DNA damage response. Promotes ubiquitination of PCNA following UV irradiation and may regulate recruitment of polymerase eta and rad51 to chromatin after DNA damage. May function as transcriptional cofactor in TGF beta signaling. Accentuates smad2-dependent transcription. Interacts with smad2 via its last three BRCT domain-containing regions in an activin signal-dependent manner. Maternally expressed, expression declines during gastrulation and continues at a lower level until late stages. Ubiquitously expressed at gastrula stage. Later in development, becomes enriched in the head and brain.