Virion-associated and cellular RNA methylase activity in normal and neoplastic mammary tissue from mammary tumor virus-infected and -uninfected mice.

ABSTRACT

A comparison of cellular RNA methylase activities and patterns between normal and neoplastic mouse mammary tissue indicated the following. The rna methylases of mammary tumor tissue extracts are qualitatively different from those of normal lactating mammary tissue, based on differences in extent of methylation; the normal lactating tissue extracts have a greater capacity of methylate RNA than do the tumor extracts studied to date. There is no correlation between capacity and either the malignant state or the etiological agent. There is a qualitative effect on methylation patterns attributable to the presence of virus. Finally, both the etiological agent, mouse mammary tumor virus, and its putative nucleoprotein core, intracytoplasmic A particles, have a N-2-guanine RNA methyltransferase integrally associated with them. These conclusions are consistent with the aberrant nucleic acid methylation hypothesis, with the reservation that aberrant does not imply hypermethylation.