Serine phosphorylation - Most of the seven STATs (except STAT2) undergo serine phosphorylation.[1] Serine phosphorylation of STATs has been shown to reduce gene transcription.[12] It is also required for the transcription of some target genes of the cytokines IL-6 and IFN- γ.[3] It has been proposed that phosphorylation of serine can regulate STAT1 dimerization,[9] and that continuous serine phosphorylation on STAT3 influences cell division.[13]