Genetic and physical linkage of exogenous sequences in transformed cells

The calcium phosphate precipitation method of Graham and van der Eb (1973) is an efficent means of introducing DNA into culturaed animal cells. Cells which incorporate one selectable marker are also likely to incorporate one selectable marker are also likely to incorporate sequences from the carrier DNA. Both selected and unselected markers are found integrated in the high molecular weight nuclear DNA of the host. In the present study, we demonstrate that exogenously acquired sequences are gentically linked, segregating and amplifying coordinately, and that their flanking sequences derive primarily from the carrier species rather than the host species. Based on these results, we propose that, upon transformation, the host cell ligates incorporated DNA into a large concatameric structure which may at times be as large as 2000 kilobases. From blotting data alone we cannot determine whether this structure is chromosomal or extrachromosomal in location.