EXPRESSION OF SEVERAL AMPLIFIED GENES IN AN ADENYLATE-DEAMINASE OVERPRODUCING VARIANT OF CHINESE-HAMSTER FIBROBLASTS

Unstable variants with increasing amounts of adenylate-deaminase (AMPD) were stepwise recovered from Chinese hamster fibroblasts plated in selective medium containing increasing coformycin concentrations; several polypeptides accumulate in the variants in parallel to AMPD: they are no longer detectable in cells which reverted to the wild-type enzyme level. The molecular cloning of c[complementary]DNA sequencies complementary to mRNA coding for 4 such polypeptides is reported. The plasmidic probes were exploited to characterize their complementary mRNA and to quantify the copies of these cognate genes in a variant and in 2 revertant clones. Different mRNA code for the 4 polypeptides; their accumulation is accounted for by amplification of their specific genes; these observations suggest that cells overproducing AMPD are characterized by the presence of amplification units comprising seveal expressed genes.