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Fig. 2 | Genes and Environment

Fig. 2

From: Transgenic rat models for mutagenesis and carcinogenesis

Fig. 2

Mutant selection for gpt delta rats. a gpt selection. The E. coli gpt gene encodes guanine phosphoribosyl transferase, which attaches a phosphoribose to 6-TG. The phosphoribosylated 6-TG is further phosphorylated and finally incorporated into DNA. Incorporation of 6-TG is toxic to E. coli and cell death is induced. Therefore, only when the gpt gene is inactivated by mutations, E. coli can make colonies on a plate containing 6-TG. b Spi- selection. The wild-type lambda phages lyse E. coli, thereby making phage plaques. However, if the E. coli chromosome harbors P2 phage DNA, which is called P2 lysogen, the wild-type lambda phage can’t lyse P2 lysogen. Only the defective lambda phage whose red and gam genes are inactivated can lyse P2 lysogen. The resulting plaques are called P2 plaques. Because the red and gam genes are localized in lambda genome side by side, the inactivation of two genes are most likely induced by deletions in the region

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