FIG. 1.

E1B-55K and E4orf6 proteins colocalize in the nuclei of rodent cells containing the RUNX1 locus of human chromosome 21. (A) Mouse A9 cells containing human chromosome 21 were infected with the recombinant vaccinia virus vTF7.3 to express the T7 RNA polymerase. The cells were transfected with cDNA for E1B-55K and E4orf6 under the control of the T7 promoter. At 12 hpi, double-label immunofluorescence was used to identify cells expressing both E4orf6 and E1B-55K. (A) Representative micrographs showing the localization of the E1B-55K protein, in which the localization was identified as predominantly cytoplasmic (a to d) or predominantly nuclear (e to h). The bar represents 5 μm. (B) Hamster (black) and mouse (gray) cells containing portions of human chromosome 21 were infected and transfected as described for panel A. At least three independent experiments were scored for the nuclear localization of E1B-55K. Cell lines that demonstrated the nuclear localization of E1B-55K in the presence of E4orf6 are indicated by a plus sign. (C) The portion of human chromosome 21 DNA in the 21q+ and MRC-2G hamster cells at the distal breakpoint is represented by black bars. Chromosome 21 is represented by the gray bar; the scale is indicate in megabase pairs. The approximate locations of STS markers are indicated. The RUNX1 gene is represented by the arrow; open boxes identify the two RUNX1 promoters.