title: Base composition studies on mitochondrial 4 S RNA from rat liver and Morris hepatomas 5123D and 7777.
abstract: The major and modified base composition of mitochondrial 4 S RNA from rat liver and from Morris hepatomas 5123D and 7777 has been determined for 16 constituents using a chemical tritium-derivative method. The base composition of these mitochondrial 4 S RNA preparations was compared with the base composition of cytoplasmic and bacterial (Escherichia coli B and Bacillus subtilis) 4-S RNAs. The results of these studies are: 1. When compared with cytoplasmic 4 S RNA, the liver and hepatoma mitochondrial 4-S RNAs are characterized by high (A + U)/(G + C) ratios and low overall degrees of base methylation and modification. 2. The mammalian mitochondrial 4-S RNAs are qualitatively even more different from the bacterial 4-S RNAs than from their cytoplasmic counterparts. Thus, several modified constituents found in both cytoplasmic and mitochondrial 4 S RNA are absent from the bacterial 4-S RNAs. 3. Mitochondrial 4S RNA from both hepatomas was found to be under-methylated and undermodified when compared with normal liver mitochondrial 4S RNA. This trend is more pronounced for the rapidly growing hepatoma 7777 (i.e., 17% undermethylation) than for the more slowly growing hepatoma 5123D (i.e., 8% undermethylation). These findings are discussed in relationship to (1) results of other authors on composition of mitochondrial 4 S RNA, (2) special features of structure and biosynthesis of mitochondrial 4 S RNA, (3) the possible evolutionary origin of mitochondria and (4) the possible role played by aberrant mitochondrial 4 S RNA in altered mitochondrial protein synthesis in tumors.
mesh_terms: D000818:Animals; D001412:Bacillus subtilis / Q000032:analysis; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000032:analysis*; D003593:Cytoplasm / Q000032:analysis; D004926:Escherichia coli / Q000032:analysis; D008099:Liver / Q000032:analysis; D008113:Liver Neoplasms / Q000032:analysis*; D008930:Mitochondria, Liver / Q000032:analysis*; D009374:Neoplasms, Experimental / Q000032:analysis; D012313:RNA / Q000032:analysis*; D012329:RNA, Bacterial / Q000032:analysis; D012334:RNA, Neoplasm / Q000032:analysis*; D051381:Rats; D012263:Ribonucleosides / Q000032:analysis; D013045:Species Specificity
chemical_list: D012329:RNA, Bacterial; D012334:RNA, Neoplasm; D012263:Ribonucleosides; D012313:RNA