Coordinator of PRMT5 and differentiation stimulator (COPRS)

Histone-binding protein required for histone H4 methyltransferase activity of PRMT5. Specifically required for histone H4'Arg-3' methylation mediated by PRMT5, but not histone H3'Arg-8' methylation, suggesting that it modulates the substrate specificity of PRMT5.

Specifically interacts with the N-terminus of histone H4 but not with histone H3, suggesting that it functions by promoting the association between histone H4 and PRMT5. Involved in CCNE1 promoter repression.