PR domain[note 1] zinc finger protein 9 is a protein that in humans is encoded by the Prdm9gene. The protein has histone H3(K4) trimethyltransferase activity, a KRAB domain, and a DNA-binding domain consisting of multiple tandem C2H2zinc finger (ZF) domains. PRDM9 specifically trimethylates 'Lys-4' of histone H3 during meiotic prophase and is essential for proper meiotic progression, but does not have the ability to mono- and dimethylate 'Lys-4' of histone H3. H3 'Lys-4' methylation represents a specific tag for epigenetic transcriptional activation which plays a central role in the transcriptional activation of genes during early meiotic prophase.
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