The E4 34k/ligase IV complex observed in extracts from H5dl1016-infected cells contains Cullin5. HeLa cells were Mock-, Ad5- or H5dl1016-infected and lysed in NP40 lysis buffer 20 h post-infection. 200 μg of extract was subject to IP with antibodies directed against Cullin5. Cul5-containing complexes were resolved by SDS-PAGE, Western transferred and probed for Ligase IV or E4 34k. I, 15% of input lysate; IP, immunoprecipitation using anti-Cul5 antibodies; C, control IP.