Homochromatographic and immunological analysis of controls of nucleolar gene function.

To compare regulation of nucleolar function of tumors and other tissues, it was necessary to develop assays of the fidelity of ribosomal DNA readouts. For this purpose, homochromatography analyses of complete T1 ribonuclease digestion products of the in vivo labeled 45 S preribosomal RNA were compared with those of 18S and of 28 S ribosomal RNA. Homochromatography analysis of the in vitro readout product of isolated nucleoli showed the presence of many large marker nucleotides of the in vivo 45 S preribosomal RNA. Moreover, no other large oligonucleotides were detected. The in vitro readout product of nucleolar chromatin had the same T1 ribonuclease digestion products, including the large marker of oligonucleotides. However, the in vitro readout product of nucleolar DNA contained no large marker T1 ribonuclease oligonucleotides. These results indicate that the fidelity of nucleolar readouts is controlled by regulatory proteins of the nucleolar chromatin. Differences were found in nucleolar proteins of normal rat liver and Novikoff hepatoma by immunological analyses. The possibility exists that differences in readout rates of tumor and other nucleoli are related to the protein difference detected by these immunological studies.