Yasuo Iwanami

Methylation patterns of transfer RNA from ascites hepatomas

Patterns of in vivo methylation as shown by the incorporation of a [3H]methyl group into tRNA were investigated for rat ascites hepatomas 13, 66, 108A, 7974 and normal liver. The contents of methylated ademine were in a sharp range of about 13–14% of the total methylated components in every case of hepatoma and liver, while those of the other methylated bases varied somewhat with the strain. When comparisons were made between the hepatoma and liver, the hepatomas appeared to be characterized by a diminished content of total methylated guanines. It was also conspicuous that, of the four constituents in methylated guanines, 7-methylguanine in the hepatomas was shown to give a percentage value not exceeding that in normal liver.

Interaction of lysine-rich histone and DNA in chromatin structure

The heat denaturation and renaturation curves of rat liver and ascites hepatoma (AH 108A) chromatins were measured. In these renaturation curves, there are small sigmoidal regions. These sigmoidal regions remained in redenaturation curves and were largely stable to DNAase I digestion. When the chromatins were treated stepwise with NaClO4 and lysine-rich histones were removed, the sigmoidal regions in the renaturation curves disappeared. These results suggested that the sigmoidal regions reflected the interaction of DNA and lysine-rich histones.