Western blot analysis of Rep proteins expressed in Sf9 cells by BacRep, BacRep52, or BacRep78 baculovirus helpers individually or upon co-infection with other baculovirus helpers (m.o.i. of 5 each). Lane 1, positive control (a lysate from 293 cells transfected with pIM45 [21]; lanes 2 through 6 contain lysates from Sf9 cells infected with, lane 2, BacRep; lane 3, BacRep52; lane 4, BacRep78; lane 5, BacRep78 + BacRep52; lane 6, BacRep78 + BacRep52 + BacVP + BacGFP (the latter vector also contains a strong baculovirus p10 promoter driving the GFP gene inside the transgene cassette [15]).