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The Nucleolar RNA of Minimal Deviation Hepatomas¹

Departments of Chemistry and Pathology [H.S.], Cancer Institute, Nishisugamo, Toshima-ku, Tokyo, Japan

The nucleolar RNA extracted by a sodium dodecyl sulfate-hot phenol procedure from isolated nucleoli of the Morris hepatoma 5123D had essentially the same sedimentation profile on the sucrose density gradient as that of the nucleolar RNA of normal rat liver. The kinetics of labeling of nucleolar RNA of this tumor with radioactive orotic acid was also similar to that of the normal liver.

Although the base composition of "newly-synthesized" RNA of the nucleolus of the Morris hepatoma 5123D and 7316B, as determined by 15 min pulse with orthophosphate-³²P, was completely different from that of the normal rat liver, it was very similar to that of more rapidly growing, undifferentiated tumors such as Novikoff hepatoma or Walker carcinosarcoma 256.

With a longer pulse of 60 min, the low adenine and high cytosine content characteristic of tumor nucleolar RNA was again found; this appeared to suggest that the difference in the specific activity of the four precursor nucleotide pools was not the major factor for the difference of ³²P base composition between normal and tumor tissues.

Since regenerating rat liver, as representative of rapidly growing normal cells, as well as host liver had a ³²P base composition similar to normal rat liver, this peculiarity found in tumors may be closely related to the malignant properties of the cell. The possible cause for this difference is discussed in terms of the molecular nature of nucleolar 45 S RNA.

¹ Supported in part by a Grant-in-Aid from the Ministry of Education, Japan.

Received 11/ 6/67. Accepted 2/25/68.