PIAS proteins contribute to the control of gene expression, and may be considered transcriptional co-regulators. 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. This interaction can either upregulate or downregulate transcription. For example, the activity of transcription factor p53 was stimulated after it was SUMOylated by PIASy. In contrast, the activity of transcription factor p73 was repressed after it was SUMOylated by PIAS1. One function of PIAS proteins is to relocate transcriptional regulators to different compartments within the nucleus of the cell.