FIG. 4.

The LXXLL motif proximal to the CH2A domain is required for MKP-1 nuclear targeting. (A) Sequence alignment of the NH₂ terminus of MKP-1, MKP-2, PAC-1, B23, and MKP-7 reveals a conserved LXXLL motif. The LXXLL motif is conserved in human, mouse, rat, and Xenopus (xCL100/xMKP-1) MKP-1. (B) Sequences of the LXXLL MKP-1 mutants. (C) The LXXLL motif mutants shown in panel B were expressed transiently in COS-7 cells along with GFP-MKP-1. Lysates were resolved by SDS-PAGE, and GFP expression was detected by immunoblotting with an anti-MKP-1 antibody. (D) GFP-MKP-1 or the MKP-1-LXXLL mutants were transiently expressed in COS-7 cells, and confocal imaging for the expression of GFP was performed. The inset in panel D shows a quantitative analysis of the GFP fluorescence distribution of the GFP-MKP-1(L16/17A) mutant analyzed as described in the legend for Fig. 2.