Mutations were created in 4 AU-rich regions within the terminal 144nt CSF-1 3′UTR as described in the text. Panels A&B represent results of binding of labeled wild type CSF-1 riboprobe to Hey (A) or NOSE.1 (B) protein extracts; Panels C&D represent results of binding of labeled mutant CSF-1 riboprobe to Hey (C) or NOSE.1 (D) protein extracts. Lanes 1, free riboprobe control; lanes 2, 1X probe mixed with 8 ug of protein extract; lanes 3, 3X probe mixed with 8ug of protein extract; lanes 4, 5 and 6, 1X probe mixed with 8 ug of protein extract in presence of 1500X, 770X or 390X excess cold probe, respectively.