Purine uptake by azaguanine-resistant Chinese hamster cells.

In this study the resistance of a number of lines of Chinese hamster ovary cells to azaguanine is examined. Those which are drug resistant by virtue of a deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT) fail to take up any exogenous hypoxanthine or azaguanine. A second class of drug resistant cells which grow in the reverse selective HAT medium and have levels of HPRT in the range of the wild type parent line take up these purines at lower rates than the nonresistant cells and incorporate smaller amounts of them into trichloracetic acidinsoluble constituents. The results suggest that their basis for resistance resides in lowered incorporation of azaguanine into DNA and RNA, possibly due to a mofified HPRT molecule which accepts hypoxanthine, but not azaguanine as a substrate.