 While PIAS proteins interact with at least 60 different proteins involved in transcription, they are known to act as E3 SUMO-protein ligases.In essence, the RING-finger-like zinc-binding domain of the PIAS protein assists in the attachment of a SUMO protein to the target transcription factor.Attachment of a SUMO protein to the target allows for protein–protein interaction between PIAS and the transcription factor.