sentence: For in vitro ADP-ribosylation of RhoA , 60 nM of recombinant wild-type C3bot or BC3-C3bot fusion protein was incubated with 0.4 μ M GST-RhoA , 1 μ M NAD , radioactive [ P ] NAD ( 0.5 μ Ci per sample ) , and 2 μ g BSA at 37 ° C in buffer containing 25 mM TEA , 2 mM MgCl , 1 mM DTT , and 1 mM GDP .