Analysis of UL25 in wt virions and L particles. Serial twofold dilutions of virions and L particles were prepared, and the proteins were separated by SDS-PAGE. Proteins were detected by Western blotting using antibodies against UL25, VP16, and VP23. For panel A, virions and L particles were equalized on the basis of their VP16 contents. For panel B, virions and L particles were equalized on the basis of their VP23 contents to determine whether capsid contamination of L particles accounted for the presence of UL25.