| Using an immunofluorescence analysis , we determined that ILF 3 and PRMT 1 co localize in the nucleus . ^^^ Moreover , PRMT 1 and ILF 3 co precipitate in immunoprecipitation assays and can be isolated together in `` pull down ' ' experiments using recombinant fusion proteins . ^^^ ILF 3 is a robust substrate for methylation by PRMT 1 and can modulate PRMT 1 activity in in vitro methylation assays . ^^^ Deletion studies demonstrated that the COOH terminal region of ILF 3 , which is rich in arginine , glycine , and serine , is responsible for the strong interaction between PRMT 1 and ILF 3 and is the site of ILF 3 methylation by PRMT 1 . ^^^ Because of this difference , NF 90 does not interact with PRMT 1 , is a much poorer substrate than ILF 3 for PRMT 1 dependent methylation , and does not modulate PRMT 1 enzyme activity . . ^^^ |