End-joining of DNA fragments in adenovirus transfection of human cells.

Overlapping terminal fragments of adenovirus DNA transfected into human cells either recombine to form standard unit-length genomes, or can join end-to-end to produce internally redundant, viable, genomes. The end-joining reaction in human HeLa and A549 cells is almost as efficient as the recombination reaction, and is relatively insensitive to the nature of the ends, as pairs of fragments terminating in several different single strands or in blunt ends can join. In contrast to the results from transfection with SV40, the ends are usually modified, for example by the loss of 3' single strands or the repair of 5' single strands. The ability to recover viable redundant molecules is not confined to any one area of the adenovirus genome, but can occur in the E1 and L2 regions as well as in the E2b region. The redundant genomes contain extra splice signals and may have the capacity to encode fusion proteins.