Histochemical studies on rat liver proteins during 4-dimethylaminoazobenzene carcinogenesis.

Areas of preneoplastic livers characterized by intense RNA staining apparently represent the sites of neoplastic transformation. These hyperbasophilic foci, as well as the hepatomas, showed a marked decrease in the stain ing intensity of the cytoplasmic proteins in sections stained by the mercury-bromophenol blue method or the MillÃ3nreaction. Following extraction of the RNA, how ever, protein stainability in these sites was comparable to that of surrounding parenchyma. Radioautographic studies further indicated that hyperbasophilic foci and hepatomas do not differ from the surrounding tissue in the labeling of cytoplasmic proteins by tritiated leucine. These results were interpreted as indicating the pres ence in sites of neoplastic transformation and liver tumors of some unusual RNA which binds to and masks the cytoplasmic proteins.