To determine if this interaction also occurred with native pUL21a, we performed co-immunoprecipitation assays on lysates from cells infected with wild-type virus (ADgfp), and we also included lysate from cells infected with UL21a deletion virus (ADsubUL21a) as a negative control ( Figure 1C ). Infected cells were treated with proteasome inhibitor, MG132, as pUL21a was highly unstable and otherwise could not accumulate to levels allowing reproducible detection of this interaction [29] . In the