Inhibits PRC2/EED-EZH1 and PRC2/EED-EZH2 complex function by inhibiting EZH1/EZH2 methyltransferase activity, thereby causing down- regulation of histone H3 trimethylation on 'Lys-27' (H3K27me3) (PubMed:29909548, PubMed:30923826, PubMed:31086175, PubMed:31451685). Probably inhibits methyltransferase activity by limiting the stimulatory effect of cofactors such as AEBP2 and JARID2 (PubMed:30923826). Inhibits H3K27me3 deposition during spermatogenesis and oogenesis (By similarity). {ECO:0000250|UniProtKB:B1B0V2, ECO:0000269|PubMed:29909548, ECO:0000269|PubMed:30923826, ECO:0000269|PubMed:31086175, ECO:0000269|PubMed:31451685}. This is the function of EZHIP (EZH inhibitory protein, Ensembl gene identifier ENSG00000187690).