The relative amounts of the cytoplasmic RNA species in normal, transformed and senescent cultured cell lines

Abstract

We have examined the relative quantities of 18S and 28S rRNA, 4S RNA and poly (A) + mRNA in the following cultured cells: the mouse fibroblast lines 3T3 and 3T6 in the resting (contact inhibited) and growing (sparse) states, 3T3 clones transformed with SV40 (SV3T3) and with both SV40 and polyoma (SV‐Py 3T3), hamster lung fibroblasts (V79), human cervical carcinoma cells (HeLa), and human diploid fibroblasts at early and late passage. The relative quantities of the RNA species were determined by labeling the cells to equilibrium with ³²PO₄ and measuring the amount of label in each RNA species. The ratio of mRNA to rRNA varied from 1.1% to 2.7% in the different cell lines, the more rapidly growing cell lines usually giving a higher ratio. In cells experiencing growth limitation either by contact inhibition or due to senescence, the ratio of mRNA to rRNA was about 30% lower than in the corresponding cells in the growing state. In most cell lines the ratio of 4S RNA to 18S rRNA was between 0.8 and 1.2, but in senescent fibroblasts, this ratio increased to greater than 1.7. Senescent fibroblasts also contained much more total RNA per unit of DNA than the same cells at early passage or than 3T6 or 3T3 cells.