FIG. 4.

Dependence of in vivo Ras modification on time of exposure to bacteria and bacterial concentration. (A) Time required for Ras modification. HT29 cells were incubated with no bacteria (0) or with 10⁸ CFU of strain 388 bacteria for 1, 2, or 3 h, as indicated. Ras was immunoprecipitated from cell lysates and detected by SDS-PAGE and immunoblotting. M, modified Ras; U, unmodified Ras. (B) Bacterial concentration required for Ras modification. Cells were incubated for 3 h with 0 to 10⁸ CFU of strain 388 bacteria, as indicated, and Ras modification was examined as for panel A. Molecular masses (in kilodaltons) are indicated.