Abstract
Certain areas in preneoplastic livers of rats fed the azo dye 4-dimethylaminoazobenzene are characterized by intense ribonucleic acid (RNA) staining and possibly represent the sites of neoplastic transformation. Cytoplasmic RNA responsible for increased basophilia in the hyperbasophilic foci and hepatomas was selectively extracted by incubating liver sections for short periods in solutions containing low concentrations of ribonuclease, without apparently altering basophilia in surrounding tissue. Moreover, experiments on protein staining confirmed that the RNA responsible for hyperbasophilia is the one that binds to and masks the cytoplasmic proteins in these sites. Since hyperbasophilia in sites of neoplastic transformation and liver tumors results from the presence of some RNA which is more sensitive to mild ribonuclease treatment than normally occurring RNA, it is suggested that it might be either a normal type or an altered form of RNA present in excess.