PIAS are a four-member protein family made of: PIAS1, PIAS3, PIASx, and PIASγ.[29] The proteins add a marker, called SUMO (small ubiquitin-like modifier), onto other proteins – such as JAKs and STATs, modifying their function.[29] The addition of a SUMO group onto STAT1 by PIAS1 has been shown to prevent activation of genes by STAT1.[30] Other studies have demonstrated that adding a SUMO group to STATs may block phosphorylation of tyrosines on STATs, preventing their dimerization and inhibiting JAK-STAT signalling.[31] PIASγ has also been shown to prevent STAT1 from functioning.[32] PIAS proteins may also function by preventing STATs from binding to DNA (and therefore preventing gene activation), and by recruiting proteins called histone deacetylases (HDACs), which lower the level of gene expression.[29]