Figure 2 HAT medium metabolism: principal and salvage pathways involved in the synthesis of DNA. The toxic base analog described in Table 1 can be incorporated by the salvage pathways. In mutant lines lacking either TK or HGPRT such bases cannot be incorporated and are therefore nontoxic for such mutant lines and these cells live. Growth of these mutants will not occur when aminopterin is used to block the principal pathway of synthesis of purines and pyrimidines because both enzymes are necessary. Only those hybrid cells that contain normal levels of HGPRT from the nonmutant parental B cell partner will be able to live in HAT medium and the remaining unfused myeloma cells die. HGPRT, hypoxanthine guanine phosphoribosyl transferase; PRPP, 5-phosphoribosyl-1-pyrophosphate; TK, thymidine kinase.

Table 1 Toxic base analogs and associated enzyme deficiency


Enzyme deficiency

6-Thioguanine (TG)

Hypoxanthine guanine

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