ADP-ribosylation of Rho in A5 CHO cells by C3 exoenzyme. In (A) A5 CHO cells were cultured for 24 hours in the presence of vehicle buffer or the indicated amounts of C3 exoenzyme. The cultures were then supplemented again with the same amounts of C3, and 24 hours later the cells were washed and lysates were subjected to α(³²P)ADP-ribosylation assay as described in Materials and Methods. The arrow points to the ³²P-labeled Rho band. Note that the cells that had been cultured with C3 showed a subsequent decrease in incorporation of ³²P, indicating that the Rho in these cells had become ADP-ribosylated during culture. In (B) the solid bars represent the means ± SEM of three independent experiments. The number above each bar represents the ribosylation response relative to that observed in the “No C3” control samples, which was arbitrarily assigned a value of 100%.