The C-terminal proline-rich domain of MIST is required for its negative function in NK1.1-induced IFN-γ production by NK cells. (A) Schematic representation of MIST mutants and their protein expression. DT40-ETR cells were infected with pMX-IRES-GFP retrovirus vectors encoding wild-type (WT) and MIST mutants. Cell lysates from GFP-positive cells were immunoblotted with anti-MIST and anti-GFP antibodies. (B-C) IFN-γ production by MIST-deficient NK cells (B) and CD4⁺ NKT cells (C) reconstituted with various MIST mutants. Results for mock-infected wild-type (+/+) NK cells are shown in the first panels for comparison. The numbers are the percentages of IFN-γ-producing and nonproducing cells in the GFP-positive population. The percentages of IFN-γ-producing cells in the noninfected cell population are also shown in the top left quadrant. Representative data from 2 independent experiments are shown.