A new set of positive/negative selectable markers for mammalian cells.

Five new positive and negative selectable markers were created for use in mammalian cells. Their negative selectabilities are based on the Thymidine kinase (Tk) gene of Herpes Simplex virus (HSV) or the Cytidine deaminase (codA) gene of E. coli. The markers can be selected positively by their ability to induce either Hygromycin (Hyg), neomycin (neo), puromycin (PAC) or Blasticidin S (BlaS) resistance. With these markers, two complete sets of markergenes are available that induce independent negative selectable phenotypes.