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Tumor-specific Polyadenylated RNA's from 7,12-Dimethylbenz(a)anthracene-induced Mammary Tumors Revealed through Hybridization with Fractionated Single-Copy DNA¹

Department of Cell Biology, Baylor College of Medicine, Texas Medical Center, Houston, Texas 77030

Polyadenylated (poly(A)⁺) and nonpolyadenylated (poly(A)^-) RNA fractions from primary, hormone-dependent, 7,12-dimethylbenz(a)anthracene-induced mammary tumors and normal rat mammary tissue were analyzed by molecular hybridization to determine if there is a unique class of "tissue-specific" RNA sequences. Single-copy [³H]DNA was fractionated into probes which were either depleted of midpregnant RNA sequences or complementary to these same sequences. When these probes were annealed to homologous and heterologous poly(A)⁺ RNA's, distinct sets of single-copy sequences were found in the two poly(A)⁺ RNA populations. The complexity of the "tumor-specific" sequences was about 6.7 x 10⁷ nucleotides (assuming asymmetrical transcription).

Hybridization of the poly(A)^– RNA fractions isolated from the 7,12-dimethylbenz(a)anthracene-induced tumors and the normal mammary gland to poly(A)^– complementary DNA's revealed that both tissues appear to contain a class of poly(A)^– RNA sequences which were distinct from the set of poly(A)⁺ RNA's. Both poly(A)^– RNA fractions saturated at 3% when hybridized to single-copy [³H]DNA. However, approximately 15 to 25% (minimum estimate) of the complexity of the poly(A)^– RNA was contributed by contaminating poly(A)⁺ RNA sequences. Therefore, the actual complexity of the poly(A)^– RNA fractions was 2.0 to 2.5% of the single-copy hybrid genome. Mixtures of these two RNA fractions also gave a saturation value of 3.0% when annealed to single-copy [³]DNA. This indicated that most of the poly(A)^– RNA's were similar in the neoplastic and normal mammary tissues. Although the majority of the infrequent RNA species are held in common between the two tissues, there is a distinct set of high-complexity poly(A)⁺ RNA sequences, presumably of nuclear origin, which is unique to the 7,12-dimethylbenz(a)anthracene-induced tumors. Whether these RNA's are processed and became functional messenger RNA's is not known. Presumably, they play a role in regulating the frequencies of the tissue-specific abundant and moderately abundant messenger RNA's and therefore provide one mechanism by which the concentration of specific proteins and ultimately the expression of the transformed phenotype may be regulated.

¹ This work was supported by Grant CA 16303 from the National Cancer Institute.

² Recipient of Career Development Award CA 00154 from the NIH. To whom requests for reprints should be addressed.

Received 2/12/81. Accepted 6/26/81.