ABSTRACT
Adenosine deaminase (ADA) is an enzyme of purine metabolism that is widely distributed among mammalian cells and tissues. Lack of faithful coamplification of linked genes is a problem often encountered in efforts to cotransfer and coamplify nonselectable genes of academic or commercial value using amplifiable genetic markers such as ADA or dihydrofolate reductase. The selection procedures described above have the ability to isolate from a mixed population of cells those having the highest levels of ADA activity. This feature enables the use of ADA minigenes as dominant selectable markers by making it possible to selectively isolate transformants on the basis of increased ADA activity. ADA minigenes, along with any nonselectable gene that has been cotransferred, may be selectively coamplified by growth of transformants in alanosine, adenosine, uridine, and increasing concentrations of deoxycoformycin. The selection protocols described have a number of highly desirable features that facilitate the use of ADA as a dominant amplifiable genetic marker.
