ABSTRACT
During eight successive isologous passages of hepatoma induced in male C3HA mice by N-nitrosodiethylamine, no common features of tumor progression were observed, although both the mitotic pattern and ploidy differed from generation to generation. These additional cytologic criteria allowed the biochemical examination of material least changed due to tumor progression. Tumor nDNA's were characterized by greater actinomycin D (AD)- and acridine orange (AO)-binding abilities than were normal nDNA's; this could have resulted from a higher proportion of double-stranded regions in tumor DNA. Isolated tumor deoxyribonucleoprotein had both lower template activity in an RNA polymerase system and fewer AD- and AO-binding sites, when compared with the activity and sites from normal mouse liver. RNA-DNA hybridization data with the above-mentioned findings showed that in hepatoma, part of the nuclear genome was repressed. Also, RNA "new classes" appeared and a certain proportion of nuclear genes controlling mitochondrial protein biosynthesis were derepressed in tumor mitochondria. The hybridization of mitochondrial RNA (mtRNA) and DNA revealed new classes of pulse-labeled RNA's in in vitro-incubated liver mitochondria that were absent from intact cell organelles; the hybridization properties of in vivo- and in vitro-formed hepatoma mtRNA's were similar. Competition and hybridization experiments demonstrated that in tumor mitochondria in vivo, some new classes of RNA existed. Hepatoma mitochondrial mRNA had a higher metabolic stability than did normal mRNA.
