Histochemical and biochemical analyses were carried out to determine what proportion of the cellular RNA is responsible for the hyperbasophilic properties of cancer cells. Sections from normal, regenerating, cirrhotic, and neoplastic livers were submitted to mild ribonuclease (RNase) treatment, which abolishes hyperbasophilia, or to perchloric acid treatment for total RNA extraction. The amounts of digested material were estimated by ultraviolet spectrophotometry.

The mild RNase treatment extracted 4 to 10% of total RNA from sections of the various control livers. With sections of rat hepatomas, on the other hand, 25% of the total RNA was removed by mild RNase treatment, and cytoplasmic hyperbasophilia was abolished in stained tissue sections. The highly sensitive RNA particular to tumor cells would thus represent approximately 18% of total tumor RNA and 24% of cytoplasmic RNA. These results indicate that hepatomas differ from normal and control livers by their high proportion of cytoplasmic RNA, possibly ribosomal RNA, showing increased sensitivity to attack by RNase and greater affinity for basic dyes.

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This investigation was supported by grants from the National Cancer Institute of Canada, and also by grants from La Foundation J. H. Biermans and Les Foundations J. Rhéaume.

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