FIG. 4.

Formation of supernatant virions. RNA was isolated from virion pellets after ultracentrifugation of cell culture supernatants from passage experiments (Fig. 3) and was analyzed by Northern hybridization with a CAT gene-specific DNA probe. In all passages with SAD Ambi-CAT HV, SDI-CL(NP) virion RNA was detectable. With increasing amounts of mini-RNA, the amount of SAD Ambi-CAT HV decreased after the passage 2 (2.P) and was not detectable after the passage 3 (3.P). In supernatants from SAD L16/SDI-CL(NP)-infected cells or in supernatants from cells infected with SDI-CL(NP) alone, mini-RNAs were not detectable. n.d., not detectable.