Patterns of integration of viral DNA in adenovirus type 2-transformed hamster cells

The patterns of integration of viral DNA in five lines of adenovirus type 2-transformed hamster cells have been investigated. Cell lines HE1 to HE5 were obtained by in vitro transformation of hamster embryo cells by ultraviolet light-inactivated Ad2^† † Abbreviations used: Ad2, adenovirus type 2; Ad12, adenovirus type 12; Ad5, adenovirus type 5.. In all lines, segments in the central parts of the viral genome are missing. The lines HE1, HE2, HE3, HE4 and HE5 contain 2 to 4, 2 to 4, 6 to 10, about 10, and 2 to 3 genome fragment equivalents per cell, respectively. The patterns of integration in lines HE2 and HE3 are identical; however, the viral genome has been amplified in these cell lines to different extents. This result provides evidence for the post-integrational amplification of inserted viral genomes. It is also conceivable that line HE2 may have undergone losses of integrated Ad2 genomes. The persisting Ad2 genomes in lines HE2 and HE3 have deletions in parts of the EcoRI F and D fragments. The remainders of these fragments are linked to cellular DNA. The termini of the segments of the viral genome have been inverted and linked to each other. This linkage could have occurred via a circular intermediate in integration or via tandemly integrated viral genomes with subsequent deletion events. The linkage of the termini of viral DNA might be mediated by short sequences of cellular DNA. In line HE5, approximately 40% of the Ad2 genome is deleted, and the truncated segments, again comprising the terminal Ad2 DNA fragments, have been fused. The termini of the viral DNA are linked to cellular DNA. In lines HE1 and HE4 complex deletion and fusion events have altered the inserted Ad2 genomes.