Differential induction by cadmium of a low-complexity ribonucleic acid class in cadmium-resistant and cadmium-sensitive mammalian cells.

The Chinese hamster ovary (CHO) cell line and the subline Cdr20F4 have been used to compare cadmium-induced ribonucleic acid (RNA) synthesis in cadmium-sensitive and cadmium-resistant cells, respectively. Gel electrophoresis of the cell-free translation products directed by polyadenylated [poly(A+)] messenger RNA (mRNA) from cadmium-induced Cdr20F4 cells revealed four low molecular weight species (Mr 7000-21 000), including metallothionein, whose synthesis was not detected after translation of either cadmium-induced or uninduced CHO cell poly(A+) mRNA. At least two of these species were also detected after translation of an abundant 400-nucleotide (NT) RNA class purified from the cadmium-induced Cdr20F4 cell RNA. Molecular hybridization of complementary deoxyribonucleic acid (cDNA) complementary to this abundant, cadmium-induced 400-NT RNA fraction indicates that the cadmium-induced RNA class possesses a total kinetic complexity of about 2000 NT's. At least half of these inducible sequences are also represented constitutively in less abundant RNA classes of both uninduced CHO and Cdr20F4 cells. Induction of Cdr20F4 cells with cadmium increases the cellular concentration of the 2000-NT-complexity RNA class to a level at least 2 x 10(3)-fold greater than its constitutive level in uninduced Cdr20F4 cells. Induction of CHO cells with cadmium increases the cellular concentration of a subset of the sequences in the 2000-NT-complexity class, but only to a level 100-fold over the constitutive level in uninduced CHO cells. The remainder of these sequences belongs to the least abundant CHO cell poly(A+) RNA class.