Fig. 3. Relocalization of FP-PP1 and FP-PP1 by overexpression of a targeting subunit. Co-expression of EYFP-PP1 and ECFP-NIPP1 in transiently transfected HeLa cells leads to retargeting of both the isoform (A) and the isoform (E) to nuclear speckles, where NIPP1 accumulates (B and F). An ECFP fusion of the NIPP1(V201K/F203K) mutant that still accumulates at speckles (D and H), but does not interact strongly with PP1 in vitro (Trinkle-Mulcahy et al., 1999), was not able to retarget either isoform (C and G). Arrows indicate nuclear speckles, whereas arrowheads indicate nucleoli. Scale bars are 10 µM.